borrowed from Latin aemulus "striving to equal or surpass, rivaling, envious," (as noun) "rival, competitor," of uncertain origin
The adjective/noun aemulus appears to be formed from an otherwise unattested verbal base aem- and the suffix -ulus, denoting inclination or repetitive action (cf. crēduluscredulous, garrulusgarrulous). Alternatively the formation has been taken as a diminutive of a noun base *aim-o- going back to a putative Indo-European *h2eim-o- "imitation," though the evidence for such a root outside Latin is exiguous, consisting solely of Hittite hima-, himma- "substitute, replica, toy." See also image entry 1, imitate.