insobriety (n.)

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., sobriete, "moderation in desires; temperate in indulgence," from Old French sobriete "sobriety, moderation" (Modern French sobrieté) or directly from Latin sobrietatem (nominative sobrietas) "moderation, temperance," from sobrius "not drunk, temperate, moderate, sensible" (see sober (adj.)). The meaning "steadiness, gravity" is recorded from 1540s. Soberness is older. Also earlier in Middle English was sobrete (c. 1300, from Old French) in the same sense, also "unintoxicated condition."