Today’s Greektionary daily words email contained κλεφτά, which jumped out at me.  It means “stealthy”, so I wondered if it might be related to klepto-.  A little searching revealed that Greek for “thief” is κλέφτης.  It makes be wonder if there was a p=>f transition from ancient Greek to modern Greek?  If anyone would know, this group would.

Yes, it’s automatic before voiceless consonants.  (In spoken Demotic Greek, that is; in lots of words artificially maintained in their ancient state by Katharevousa, the purist form of the language, the p is kept.)