BEHOLD, We have bestowed upon thee good in abundance:1
hence, pray unto thy Sustainer [alone], and sacrifice [unto Him alone].
Verily, he that hates thee has indeed been cut off [from all that is good]!2
The term kawthar is an intensive form of the noun kathrah (Zamakhshari), which, in its turn, denotes "copiousness", "multitude" or "abundance"; it also occurs as an adjective with the same connotation (Qamus, Lisan al-'Arab, etc.). In the above context, which is the sole instance of its use in the Qur'an, al-kawthar obviously relates to the abundant bestowal on the Prophet of all that is good in an abstract, spiritual sense, like revelation, knowledge, wisdom, the doing of good works, and dignity in this world and in the hereafter (Razi); with reference to the believers in general, it evidently signifies the ability to acquire knowledge, to do good works, to be kind towards all living beings, and thus to attain to inner peace and dignity.
Lit., "it is he that is cut off (abtar)". The addition, between brackets, of the phrase "from all that is good" is based on an explanation forthcoming from the Qamus.