early 15c., from Old French incomparable (12c.) or directly from Latin incomparabilis "that cannot be equaled," from in- "not" (see in- (1)) + comparabilis "comparable" (see comparable). Related: Incomparably.
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.
"capable of being compared," early 15c., from Old French comparable, from Latin comparabilis "capable of comparison," from comparare "make equal with, liken, bring together for a contest," from com "with, together" (see com-) + par "equal" (see par (n.)). Related: Comparably; comparability.