epicycle n.

before vowels reduced to ep-, before aspirated vowels eph-, word-forming element meaning "on, upon, above," also "in addition to; toward, among," from Greek epi "upon, at, close upon (in space or time), on the occasion of, in addition," also "after," from PIE *epi, *opi "near, at, against" (source also of Sanskrit api "also, besides;" Avestan aipi "also, to, toward;" Armenian ev "also, and;" Latin ob "toward, against, in the way of;" Oscan op, Greek opi- "behind;" Hittite appizzis "younger;" Lithuanian ap- "about, near;" Old Church Slavonic ob "on"). A productive prefix in Greek; also used in modern scientific compounds (such as epicenter).

also *kwelə-, Proto-Indo-European root meaning "revolve, move round; sojourn, dwell."

It forms all or part of: accolade; ancillary; atelo-; bazaar; bicycle; bucolic; chakra; chukker; collar; collet; colonial; colony; cult; cultivate; culture; cyclamen; cycle; cyclo-; cyclone; cyclops; decollete; encyclical; encyclopedia; entelechy; epicycle; hauberk; hawse; inquiline; Kultur; lapidocolous; nidicolous; palimpsest; palindrome; palinode; pole (n.2) "ends of Earth's axis;" pulley; rickshaw; talisman; teleology; telic; telophase; telos; torticollis; wheel.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit cakram "circle, wheel," carati "he moves, wanders;" Avestan caraiti "applies himself," c'axra "chariot, wagon;" Greek kyklos "circle, wheel, any circular body, circular motion, cycle of events,"polos "a round axis" (PIE *kw- becomes Greek p- before some vowels), polein "move around;" Latin colere "to frequent, dwell in, to cultivate, move around," cultus "tended, cultivated," hence also "polished," colonus "husbandman, tenant farmer, settler, colonist;" Lithuanian kelias "a road, a way;" Old Norse hvel, Old English hweol "wheel;" Old Church Slavonic kolo, Old Russian kolo, Polish koło, Russian koleso "a wheel."