word-forming element meaning "not, opposite of, without" (also im-, il-, ir- by assimilation of -n- with following consonant, a tendency which began in later Latin), from Latin in- "not," cognate with Greek an-, Old English un-, all from PIE root *ne- "not."
In Old French and Middle English often en-, but most of these forms have not survived in Modern English, and the few that do (enemy, for instance) no longer are felt as negative. The rule of thumb in English has been to use in- with obviously Latin elements, un- with native or nativized ones.
1620s, "well-put or applied, appropriate," from Latin appositus, adpositus "contiguous, neighboring;" figuratively "fit, proper, suitable," past participle of apponere "lay beside, set near," especially "serve, set before," also "put upon, apply," from ad "to, toward" (see ad-) + ponere "to place" (past participle positus; see position (n.)).
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<a href="https://www.etymonline.com/word/inapposite">Etymology of inapposite by etymonline</a>
Harper, D. (n.d.). Etymology of inapposite. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/inapposite