Renee of Glosses.net has a very interesting entry today on the Russian word that was originally keif and is now kaif (when and why did it change?); it’s from the Arabo-Persian keyf ‘opiate; intoxication; pleasure, enjoyment’ (borrowed into English in various forms, listed in the OED as kef ‘a state of drowsiness or dreamy intoxication, such as is produced by the use of bhang; the enjoyment of idleness; dolce far niente’). The word was used by Dostoyevsky, Chekhov, and others, but it’s come down in the world, as Renee says:
Today ‘kajf’ is famous from the jargon of narkomany (drug abusers), where it can denote any drug. But kajf is in no way limited to drug culture. Poimal kaif/slovil kaif lit. “caught some kajf” is “I had fun”. The expression v kaif as in eto mne v kaif ‘this is fun to me’ is extremely prolific (about 790 Google hits today). Two frequent verbal formations from kajf [are] kajfovat’ “to have fun/ to be high” and kajfanut’ “to get high”.
Incidentally, shortly after the entry kef in the OED comes kehaya ‘a Turkish viceroy, deputy, agent, etc; a local governor; a village chief.’ You’d never know it, but it turns out to be from Persian katkhuda ‘viceroy, vicar, deputy,’ which itself is perfectly straightforward: kad ‘house’ + khuda ‘master.’