1540s, "separate (someone or something) from a generally body or class of things," from Latin segregatus, past participle of segregare "set apart, lay aside; isolate; divide," literally "separate from the flock," from *se gregare, from se "apart from" (see se-) + grege, ablative of grex "herd, flock" (from PIE root *ger- "to gather").

Originally often with reference to the religious notion of separating the flock of the godly from the sinners, later scientifically in reference to classifications. In modern social context, "to force or enforce racial separation and exclusion," by 1898. Intransitive sense of "separate, go apart" is by 1863. Related: Segregated; segregating.

"having the power or tendency of separating," 1580s, from Medieval Latin segregativus, from Latin segregare "set apart, lay aside; isolate; divide" (see segregate (v.)).

1550s, "act of separating" (a sense now obsolete); 1610s, "act or action of segregating, separation from others," from Late Latin segregationem (nominative segregatio), noun of action from past-participle stem of segregare (see segregate). Meaning "state or condition of being segregated" is from 1660s. Specific U.S. sense of "enforced separation of races" is attested from 1883.

Proto-Indo-European root meaning "to gather." 

It forms all or part of: aggregate; aggregation; agora; agoraphobia; allegory; category; congregate; cram; egregious; gregarious; panegyric; paregoric; segregate.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit gramah "heap, troop;" Greek ageirein "to assemble," agora "assembly;" Latin grex "flock, herd," gremium "bosom, lap;" Old Church Slavonic grusti "handful," gramota "heap;" Lithuanian gurgulys "chaos, confusion," gurguolė "crowd, mass;" Old English crammian "press something into something else."

1947 (the policy was officially begun 1948), "segregation of European from non-European people in South Africa," from Afrikaans apartheid (1929 in a South African socio-political context), literally "separateness," from Dutch apart "separate" (from French àpart; see apart) + suffix -heid, which is cognate with English -hood. The official English synonym was separate development (1955).

"Segregation" is such an active word that it suggests someone is trying to segregate someone else. So the word "apartheid" was introduced. Now it has such a stench in the nostrils of the world, they are referring to "autogenous development." [Alan Paton, New York Times, Oct. 24, 1960]