Origin and history of immaterial

mid-14c., "real, ordinary; earthly, drawn from the material world" (contrasted with spiritual, mental, supernatural), a term in scholastic philosophy and theology, from Old French material, materiel (14c.) and directly from Late Latin materialis (adj.) "of or belonging to matter," from Latin materia "matter, stuff, wood, timber" (see matter (n.)).

From late 14c. as "made of matter, having material existence; material, physical, substantial." From late 15c. as "important, relevant, necessary, pertaining to the matter or subject;" in the law of evidence, "of legal significance to the cause" (1580s).

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.