active word-forming element in English and in many verbs inherited from French and Latin, from Latin de "down, down from, from, off; concerning" (see de), also used as a prefix in Latin, usually meaning "down, off, away, from among, down from," but also "down to the bottom, totally" hence "completely" (intensive or completive), which is its sense in many English words.
As a Latin prefix it also had the function of undoing or reversing a verb's action, and hence it came to be used as a pure privative — "not, do the opposite of, undo" — which is its primary function as a living prefix in English, as in defrost (1895), defuse (1943), de-escalate (1964), etc. In some cases, a reduced form of dis-.
late 15c., "to make conditions, stipulate," from condition (n.). Meaning "subject to something as a condition" is from 1520s; sense of "form a prerequisite of" is from 1868. Meaning "to bring to a desired condition" is from 1844; psychological sense of "teach or accustom (a person or animal) to certain habits or responses" is from 1909. Related: Conditioned; conditioning.
<a href="https://www.etymonline.com/word/decondition">Etymology of decondition by etymonline</a>
Harper, D. (n.d.). Etymology of decondition. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/decondition