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.
early 15c., "beneficial, convenient," from Old French commodios and directly from Medieval Latin commodiosus "convenient, useful," from Latin commodus "proper, fit, appropriate, convenient, satisfactory," from com-, here perhaps an intensive prefix (see com-), + modus "measure, manner" (from PIE root *med- "take appropriate measures"). Meaning "conveniently roomy, spacious" is attested from 1550s. Related: Commodiously; commodiousness.
<a href="https://www.etymonline.com/word/incommodious">Etymology of incommodious by etymonline</a>
Harper, D. (n.d.). Etymology of incommodious. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/incommodious