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.
mid-15c., "having an inferior rank," from Medieval Latin subordinatus "placed in a lower order, made subject," past participle of subordinare "place in a lower order," from Latin sub "under" (see sub-) + ordinare "arrange, set in order," from ordo (genitive ordinis) "row, rank, series, arrangement" (see order (n.)). Related: Subordinance; subordinant; subordinately. For "of or pertaining to the classificatory rank of a suborder," subordinal (1842) is used.
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<a href="https://www.etymonline.com/word/insubordinate">Etymology of insubordinate by etymonline</a>
Harper, D. (n.d.). Etymology of insubordinate. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/insubordinate