admixture (n.)

c. 1600, "act of mingling," with -ure + admix (1530s), a back-formed verb from admixt "mingled" (early 15c.), a past-participle adjective from Latin admixtus "mixed with," past participle of admiscere "to add to by mingling, mix with," from ad "to" (see ad-) + miscere "to mix" (see mix (v.)). In Middle English admixt was mistaken as the past participle of a (then) non-existent *admix. The earlier noun was admixtion (late 14c., from Latin admixionem).