c.1600, with -ure, from admix (1530s), a back-formation from admixt (early 15c.), 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). In Middle English admixt was mistaken as a past participle of a (then) non-existent *admix. Earlier in this sense was admixtion (late 14c.).