late 15c. (Caxton), "destroy or derange the order of, throw into confusion," from dis- "not" (see dis-) + order (v.). Replaced earlier disordeine (mid-14c.), from Old French desordainer, from Medieval Latin disordinare "throw into disorder," from Latin dis- + ordinare "to order, regulate," from ordo (genitive ordinis) "row, rank, series, arrangement" (see order (n.)). Related: Disordered; disordering.

early 15c., "in, of, or pertaining to the mind; characteristic of the intellect," from Late Latin mentalis "of the mind," from Latin mens (genitive mentis) "mind," from PIE root *men- (1) "to think."

In Middle English, also "of the soul, spiritual." From 1520s as "done or performed in the mind." Meaning "crazy, deranged" is by 1927, probably from combinations such as mental patient (1859); mental hospital (1891). Mental health is attested by 1803; mental illness by 1819; mental retardation by 1904.

1520s, "lack of regular arrangement;" 1530s, "tumult, disturbance of the peace;" from disorder (v.). Meaning "an ailment, a disturbance of the body or mind" is by 1704.

late 13c., "mental distress, emotional disorder of the mind, grief," from Old French destorbance (12c., Old North French distorbance), from destourber, from Latin disturbare "throw into disorder," from dis- "completely" (see dis-) + turbare "to disorder, disturb," from turba "turmoil" (see turbid).

Meaning "public disturbance, political agitation" is from c. 1300; that of "violent interruption of peace or unity" is late 14c.; it is the sense in disturbance of the (king's) peace," early 15c.

late 14c., perturbacioun, "mental disturbance, state of being perturbed," from Old French perturbacion "disturbance, confusion" (14c.) and directly from Latin perturbationem (nominative perturbatio) "confusion, disorder, disturbance," noun of action from past participle stem of perturbare (see perturb).

c. 1300, confusioun, "overthrow, ruin," from Old French confusion "disorder, confusion, shame" (11c.) and directly from Latin confusionem (nominative confusio) "a mingling, mixing, blending; confusion, disorder," noun of action from past-participle stem of confundere "to pour together," also "to confuse" (see confound).

Meaning "act of mingling together two or more things or notions properly separate" is from mid-14c. Sense of "a putting to shame, perturbation of the mind" (a sort of mental "overthrow") is from c. 1400 in English, while that of "mental perplexity, state of having indistinct ideas" is from 1590s. Meaning "state of being mixed together," literally or figuratively, "a disorderly mingling" is from late 14c.

"a physical disorder or disease," late 13c., maladie, from Old French maladie "sickness, illness, disease" (13c.), abstract noun from malade "ill" (12c.), from Late Latin male habitus "doing poorly, feeling sick," literally "ill-conditioned," from Latin male "badly" (see mal-) + habitus, past participle of habere "to have, hold" (from PIE root *ghabh- "to give or receive"). Extended sense of "moral or mental disorder, disordered state or condition" is from 14c. Related: Maladies.

"mental disorder characterized by systematized delusions of more or less definite scope," 1848 (earlier paranoea 1811), from Greek paranoia "mental derangement, madness," from paranoos "mentally ill, insane," from para- "beside, beyond" (see para- (1)) + noos "mind," which is of uncertain origin.

FOR several years frequent descriptions have been given in the foreign journals, especially German and Italian, of the forms of insanity designated by the names Paranoia, Verrücktkeit, and Wahnsinn. ["Paranoia — Systematized Delusions and Mental Degenerations," J. Séglas (transl. William Noyes), 1888]