inaccessible (adj.)

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.

c. 1400, "affording access, capable of being approached or reached," from Old French accessible and directly from Late Latin accessibilis, verbal adjective from Latin accessus "a coming near, an approach; an entrance," from accedere "approach, go to, come near, enter upon" (see accede). The meaning "easy to reach" is from 1640s; of art or writing, "able to be readily understood," by 1961 (a word not needed before writing or art often deliberately was made not so). Related: Accessibility.