(1) Kush was the name of one of the two sons of Raam and Seetaa, the other was Lav.
(2) The word Kush is a variant of actual Arabic word Kuss meaning homicide. European cartographers too spelled according to the Indian accent. The same Kuss gives us Urdu word Khud-kusse (or Khud-Kushee), i.e. self-killing.
(3) Hindu-kush Parvat - It is important to note that the name "Hindu Kush" only comes into use after the Islamic invasions commencement.

(4) Kush or Kushaa - a kind of grass which is used by Hindu in their religious activities. Thee are three types of grass used by Hindu in their religious activities - Darbhaa grass, Kush grass, and Doorvaa grass. Although Darbhaa grass is considered very holy and it should be used where it is available; but when Darbhaa grass is not available one may use Kush or Kushaa grass; or when Kush grass is not available one may use Doorvaa (argumpill) grass, and if even Doorvaa grass is not available oe may use normal grass. Kush grass is considered holy because Garud Jee placed the Amrit Kalash on the blades of Kush grass when he brought it to free his mother Vinataa from the slavery of her sister Kadroo.

This grass is generally used in religious Hom (Yaga) and Pitri Karm. It is said that no sacred activity is sacred without this grass. Braahman always keep this grass with them, because it is used in many kinds of activities for purification. Kush in Sanskrit language means "sharp" in the sense of keen intelligence or Kushal (expert). Its blades grow in pairs along the tall stems are very sharp. So lie the sword it denotes the discriminatory power - wisdom. It is an age old tradition to cover the food with Kush grass during the Solar eclipse to protect them from harmful ultra violet rays. Its oil can be used in Summer for its cooling effect. Even Kush flavored Sharbat (syrup) is used for its cooling effect.

Puraan say that it was formed when the hairs on Koorm Avataar were loosened during the churning of Ocean and got washed away to the shore and became as Kush grass. Later when Amrit came out of the Ocean, some of its drops fell on this grass also, that is why it became more sacred. Kush grass is identified with Vishnu and is believed to have the power of purifying anything. It was used to make ritual seat (Aasan) as far as back to Ved period.

Excerpts from the book "The Great Hindu Tradition"
Also called as Darbhaa or Doorvaa grass. It is a grass leaf and its role and place in a Braahman’s life is supreme. It is considered as a form of wealth and can cleanse us of our sins as it has the power to purify. We must have at least basic knowledge about this holy grass leaf.

There are several types of grass that can be used such as Darbhaa, Vishwaamitra, Moonj, Sara etc. The botanical name of Darbhaa is "Poa Cynosuroides". Even modern researchers speak of its special characteristics and the power of its vibrations. Tradition avers that Brahmaa Jee resides at the roots of Kush grass, Keshav in the centre and Shankar in the tip; and other Gods in the four directions – as in the case of a Peepal tree. Great sages like Harit, Maarkandeya, Atri, Kaushik, Vyaas, Saataatapa, Yaagyavalkya, Ashwaalaayan and Aapastambh have eulogized Darbhaa. Though there are minor variations in the use ofKush in Dev Karm and Pitri Karm, there is unison among all the Rishi in underscoring the place of Kush in all rites and rituals. Our Ved talk about it, and there are many Pauranik stories woven around Kush grass.

(1) The Ved too speak specifically of the value of Kush : the Achchhidra section of Krishn Yajur Ved Braahman is a case in point.
(2) The ancient texts of Saar Samuchchaya, Smriti Saar, Smriti Ratn, Smriti Chintaamani, Smriti Bhaaskar and Vishnu Puraan.
(1) The Mahaabhaarat cites a story of Garud, the mythic bird and Vishnu’s vehicle bringing ambrosia and the serpents getting their tongue split lengthwise when they licked the Kush grass on which a few drops of the ambrosia fell.
(2) Raamaayan also cites a story in which Raam aims a Kush straw arrow at Jayant who came in the shape of a crow.
(3) In Raamaayan, Seetaa always put a Kush grass blade when She talked to Raavan.
(3) In the story of Mahaa Bali, Vaaman Avataar clears the spout of pitcher with a blade of Kush grass.

How to Wear this Grass
The Kush grass is to be worn on the ring finger of the right hand, in a circular formation, prior to starting any religious rite like Hom, Daan, Yagya – in fact any Dev or Pitri Karm. This ubiquitous adornment on the finger of the Kartaa (doer) of any ritual is called a Pavitram, and it is necessarily made only of Kush grass. There is an opinion that one can permanently wear the Pavitram on one's finger, maybe this thinking is the idea ascribed to sages like Kaatyaayan and Harit that a Pavitram could be made of gold and worn all the time, but a Pavitram made of gold cannot substitute a Kush Pavitram. When a Karm starts, one has to necessarily have a Kush Pavitram on, even if one is already wearing a Swarn Pavitram. Any reference to Pavitram means only Kush. Incidentally, when a Swarn Pavitram is worn on the ring finger, a ring called Tarjanee, made of silver, is also to be simultaneously worn on the index finger. And only the eldest son can wear the Tarjanee  and that also not when his father is alive.

Generally one does not prepare Kush for oneself. It is either received from the family Purohit or a properly qualified elderly person. Of course if the Pavitram is not available from these sources one can prepare himself for oneself. The Kush has to be fresh and the Pavitram should be prepared just before the start of a ritual – it should not be stocked.

There are restrictions in the number of Kush leaves used to prepare the Pavitram. In Vaidik recitations, meditation and for Poojaa it is prepared from 2 leaves of the grass. In all ancestral worship like Shraaddh or Amaavasyaa libations 3 leaves are used. In death rites Kush is prepared with only one leaf of the grass. Though the number of leaves may change, the shape, size and method of preparing it do not change.

The Kartaa should first do Aachaman while taking the Pavitram from his Aachaarya, preparatory to the start of the ritual. Likewise, the performance should end again with an Aachaman. On both occasions (i.e. when Aachaman is done), the Pavitram is to be positioned over the right earlobe. At the commencement of the rite, the Kartaa will do the Aachaman, take the Pavitram from the ear and wear it on his finger as described above. At the conclusion of the rite, he has to remove the Pavitram from the ear, untie it and throw it in the Nirriti (south-west) direction and do the Aachaman. If the Kartaa has to drink water during the ritual or sip milk etc as part of the ceremony, he should not drink with the Pavitram on. He should lodge it over the right earlobe and then drink. The Pavitram should not be kept elsewhere or handed over to anyone. Similarly while doing Paad Prakshaalan (a ritual of washing another person’s feet) the Pavitram must be removed from the finger and placed above the right earlobe.

Other Uses of Kush Grass
--It becomes the Aasan or seat for doing Vaidik Karm. It serves as a connecting link between husband and wife during a ritual when they do Sankalp (take a resolve to do the Karm). The wife touches her husband with Kush grass.
--At the time of temple consecration (Kumbhaabhishekam) the Kalash is connected to the idol and the tower with a rope made of Kush grass.
--Kush is believed to protect food prepared during an eclipse.
--Kush is a must in all Hom (in places like Paristheeriya, Paatra Saadhanaa, Ayaamita, Aagyaa Sanskaar, etc)
--Along with the mango leaves and coconut, a Koorcham made of Kush is also placed in the Kalash where Aavaahan is performed for Dev.
--A belt made of Kush grass is tied around the waist of the Brahmchaaree during Upanayan Sanskaar, and around the waist of the bride in her marriage ceremony.
--For Brahmaavaran (the selection of a Vidwaan or a scholar) in Hom, Kush is used.
--A small clutch of Kush is handed over to the Aachaarya to whom power of attorney is given by the Kartaa with a request that the Aachaarya may perform the proposed Jap or Hom on his behalf.

Do’s and Don’ts
--The tip of the Kush grass should always be intact. The grass leaf without the tip is useless.
--When we take Kush from a bundle, we have to pick it up from the lower/root side and not from the top.
--When we set it down, care must be taken to see that its tip faces East or North.
--The Kush should not be placed on bare earth.
--Kush grass cannot be reused; or and if it is trampled it should not be used again.
--Kush grass should not be cut with nails.

Kush grass purifies us, protects us from any mishaps during the ritual.