The adjective επιτηδειος (epitedeios) means made for a purpose in the sense of suitable or convenient or compatible (James 2:16 only). It's quite common in the classics and may describe fitness in a positive sense (of some convenient facility, useful device or welcomed provisions), or a negative sense (fit to be kicked and run off). Our word frequently describes persons in that same broad way, and could further describe such a person in the sense of them being careful or studious or even friendly and agreeable.

It's a complete mystery where our word comes from, although it obviously comprises the familiar prefix επι (epi), meaning on or upon or "for" or "in order to". The second part of our word is harder to explain, because it would involve some noun τηδος (tedos) or ταδος (tados), which otherwise does not exist either in Greek or in other Indo-European languages.

Fortunately for everybody, here at Abarim Publications we are compiling an ever growing list of words that look Greek but are really Hebrew, or could pass as Hebrew, or could be better explained as Hebrew: see our article on the many Hebrew roots of Greek. That said, the word that leaps to mind is תודה (toda), meaning thanks! It comes from the verb הוד (hod), to be worthy of praise, which in turn has to do with the verb ידה (yada), to praise, and hence of course with the names Judah and thus Jew.