It's persian (farsi) for Pimp but it has taken another tone in a common vocabulary. It can be used to replace fucker, asshole, buddy, bro. It all depends of how you use it. It can be a friendly word or a very nasty one depending to the way it is used. It's as powerful as the word fucker.
example 1 :
hey koskesh, you were supposed to call me what happened?
example 2:
that koskesh will get what he deserves
example 3:
Don't do business with that koskesh, he would sell his own mom for a buck
it has several meanings, the literal one is "cuckold"; however, the figurative sense could be used as a "noun" or "adj".
In a figurative sense, this word implies A despicablesmart-ass person who conducts unsportsmanlike behaviors toward anything such as friendship, business, etc.
The DNC chair was Koskesh! because she koskeshly put forthClinton into Democratic candidacy.