1550s in a literal sense "mix or mingle things or ideas so as to render the elements indistinguishable;" from mid-18c. in the active, figurative sense of "perplex the mind or ideas of, discomfit in mind or feeling," but not in general use until after c. 1800. From 1862 as "erroneously regard as identical." It took over these senses from its older doublet, confound (q.v.).
The past participle confused (q.v.) is attested much earlier, in Middle English (serving as an alternative past tense to confound), evidently an adaptation of Old French confus or Latin confusus, "with the native ppl. ending -ED and the present stem a much later inference from it" [OED]. Related: Confusing.
early 14c., "discomfited, routed, defeated" (of groups), serving at first as an alternative past participle of confound, as Latin confusus was the past participle of confundere "to pour together, mix, mingle; to join together;" hence, figuratively, "to throw into disorder; to trouble, disturb, upset."
The Latin past participle also was used as an adjective, with reference to mental states, "troubled, embarrassed," and this passed into Old French as confus "dejected, downcast, undone, defeated, discomfited in mind or feeling," which passed to Middle English as confus (14c.; for example Chaucer's "I am so confus, that I may not seye"), which then was assimilated to the English past-participle pattern by addition of -ed. By mid-16c., the word evolved a back-formed verb in confuse. Few English etymologies are more confusing.
Of individuals, "discomfited in mind, perplexed," from mid-14c.; in logic, "indistinct, indistinguishable from other ideas from which it ought to be different," 1610s. Meaning "lacking orderly arrangement of parts" is from 1776. Related: Confusedly.
It forms all or part of: alchemy; chyle; chyme; confound; confuse; diffuse; diffusion; effuse; effusion; effusive; fondant; fondue; font (n.2) "complete set of characters of a particular face and size of type;" found (v.2) "to cast metal;" foundry; funnel; fuse (v.) "to melt, make liquid by heat;" fusible; fusion; futile; futility; geyser; gush; gust (n.) "sudden squall of wind;" gut; infuse; ingot; parenchyma; perfuse; perfusion; profuse; refund; refuse (v.) "reject, disregard, avoid;" refuse (n.) "waste material, trash;" suffuse; suffusion; transfuse; transfusion.
It is the hypothetical source of/evidence for its existence is provided by: Greek khein "to pour," khoane "funnel," khymos "juice;" Latin fundere (past participle fusus) "melt, cast, pour out;" Gothic giutan, Old English geotan "to pour;" Old English guttas (plural) "bowels, entrails;" Old Norse geysa "to gush;" German Gosse "gutter, drain."
late 14c., perturben, "disturb greatly, disturb mentally; cause disorder in," from Old French perturber "disturb, confuse" (14c.) and directly from Latin perturbare "to confuse, disorder, disturb," especially of states of the mind, from per "through" (from PIE root *per- (1) "forward," hence "through") + turbare "disturb, confuse," from turba "turmoil, crowd" (see turbid). Related: Perturbed; perturbing.
"confound, confuse," 1852, a fantastical mock-Latin American English coinage from confound or confuse, originally in "Negro dialect" passages in works such as "J. Thornton Randolph's" pro-slavery "The Cabin and Parlor" (1852, a response to "Uncle Tom's Cabin"), picked up in London publications by the 1860s. Similar formations include confubuscate, conflabberated, etc., and compare discombobulate. Related: Confusticated; confusticating.