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.
1779, "capable of being judged or estimated," from French appréciable and directly from Medieval Latin appretiabilis, from Late Latin appretiare "set a price to" (see appreciate). The word had been used in Middle English in a sense of "worthy" (mid-15c.). Related: Appreciably.
Others are reading
<a href="https://www.etymonline.com/word/inappreciable">Etymology of inappreciable by etymonline</a>
Harper, D. (n.d.). Etymology of inappreciable. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/inappreciable