early 15c., "payment of debt or retribution;" see acquit + -al (2). Sense of "a release from debt or obligation" is from mid-15c.; that of "freeing from charge or offense" (by legal process) is from 1530s.
mid-13c., aquiten, "repay, reciprocate, reward or retaliate for" (a good or bad deed); c. 1300 as "satisfy a debt; redeem (a pledge)," from Old French aquiter, acquiter "pay, pay up, settle a claim" (12c., Modern French acquitter), from a- "to" (see ad-) + quite "free, clear," from Medieval Latin quitus, quittus, from Latin quietus "free" (in Medieval Latin "free from war, debts, etc."), also "calm, resting" (from PIE root *kweie- "to rest, be quiet"). Also in part from Medieval Latin acquitare.
From mid-14c. as "relieve (someone) of an obligation, release from a pledge," hence the meanings "set (an accused person) free from charges, pronounce not guilty," and "discharge one's duty; behave or conduct oneself" (for better or worse), all of which date to the late 14c. The notion in the word is "to release or discharge," from an obligation or from accusation, guilt, censure, or suspicion. Related: Acquitted; acquitting.
suffix forming nouns of action from verbs, mostly from Latin and French, meaning "act of ______ing" (such as survival, referral), Middle English -aille, from French feminine singular -aille, from Latin -alia, neuter plural of adjective suffix -alis, also used in English as a noun suffix. Nativized in English and used with Germanic verbs (as in bestowal, betrothal).
<a href="https://www.etymonline.com/word/acquittal">Etymology of acquittal by etymonline</a>
Harper, D. (n.d.). Etymology of acquittal. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/acquittal