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.

early 14c., "separate into parts or pieces," from Latin dividere "to force apart, cleave, distribute," from assimilated form of dis- "apart" (see dis-) + -videre "to separate," which, according to de Vaan, is from PIE *(d)uid- "to separate, distinguish" (source also of Sanskrit avidhat "allotted," Old Avestan vida- "to devote oneself to"). He writes: "The original PIE verb ... (which became thematic in Latin) meant 'to divide in two, separate'. It lost initial *d- through dissimilation in front of the next dental stop, and was reinforced by dis- in Latin ...." Also compare devise.

It is attested from late 14c. as "sever the union or connection with," also "disunite, cause to disagree in opinion." Intransitive sense of "become separated into parts" is from 1520s. Mathematical sense "perform the operation of division" is from early 15c. Divide and rule (c. 1600) translates Latin divide et impera, a maxim of Machiavelli. Related: Divided; dividing.

"quality of being distinct or individual, individuality," 1815, from individual + -ism. As the name of a social philosophy favoring non-interference of government in lives of individuals (opposed to communism and socialism) first attested 1851 in writings of J.S. Mill.

Is it not the chief disgrace in the world, not to be an unit; not to be reckoned one character; not to yield that peculiar fruit which each man was created to bear, but to be reckoned in the gross, in the hundred, or the thousand, of the party, the section, to which we belong; and our opinion predicted geographically, as the north or the south? [Emerson, "The American Scholar," 1837]

1839, "egoist, free-thinker," from individual + -ist, and compare individualism. Related: Individualistic.

1610s, "the aggregate of one's idiosyncrasies," from individual + -ity, or from Medieval Latin individualitas. Meaning "condition of existing as an individual" is from 1650s.

1630s, "to make individual, stamp with individual character;" 1650s, "to point out individually, to note separately as individuals;" see individual + -ize. Related: Individualized; individualizing.

1590s, "indivisibly," from individual + -ly (2). Meaning "as individuals" is from 1640s.

1610s, from Medieval Latin individuatus, past participle of individuare "make individual," from Latin individuus "individual" (see individual (adj.)). Perhaps modeled on obsolete French individuer. Related: Individuated; individuating.

1620s, from Medieval Latin individuationem (nominative individuatio), noun of action from past participle stem of individuare "to make individual," from Latin individuus "individual" (see individual (adj.)). Psychological sense is from 1909.