it means talking bullshit in persian (farsi). and is mostly used by the younger teen generation in iran, and is equivalent to a "shut uppp" in english.
goodarz: "bro i swear hannaneh is telling some kos-o-sher to her bestie haniyeh!"
mohsen: "don't worry about it bro she'll come to her senses.
mohsen: "don't worry about it bro she'll come to her senses.
by Ariashahanshah April 7, 2022
Get the Kos-o-shermug.