exogamy n.

word-forming element in words of Greek origin meaning "outer, outside, outer part," used from mid-19c. in scientific words (such as exoskeleton), from Greek exō (adv.) "outside," related to ex (prep.) "out of" (see ex-).

word-forming element meaning "marriage" in anthropology and "fertilization" in biology, from Greek -gamia, from gamos "marriage" (see gamete).

"marriage within the tribe or group," 1865, from endo- on model of polygamy. Related: Endogamous (1865). Opposed to exogamy. Apparently both were coined by Scottish anthropologist John Ferguson McLennan (1827-1881) in "Primitive Marriage."

To this law, the converse of caste, forbidding marriage within the tribe, Mr. M'Lennan has given the name of exogamy: while, instead of caste, since that word involves notions unconnected with marriage, he has used the correlative word — endogamy. [review in The Lancet, March 25, 1865]