inconstant 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.

late 14c., "steadfast, resolute; patient, unshakable; fixed or firm in mind," from Old French constant (14c.) or directly from Latin constantem (nominative constans) "standing firm, stable, steadfast, faithful," present participle of constare"to stand together," from assimilated form of com "with, together" (see con-) + stare "to stand," from PIE root *sta- "to stand, make or be firm."

Meaning "steadfast in attachment to a person or cause" is from early 15c. Of actions and conditions, "fixed, not varying" (1540s); "continual, enduring" (1650s). Meaning "regularly recurring" is from 1817. Related: Constantly.