Etymology
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interpersonal (adj.)
1911 (OED finds an isolated use from 1842), from inter- "between" + person (n.) + -al. Introduced in psychology (1938) by H.S. Sullivan (1892-1949) to describe behavior between people in an encounter. Related: Interpersonally.
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intervention (n.)

early 15c., intervencioun, "intercession, intercessory prayer," Late Latin interventionem (nominative interventio) "an interposing, a giving security," literally "a coming between," noun of action from past-participle stem of Latin intervenire "to come between, interrupt," from inter "between" (see inter-) + venire "to come" (from a suffixed form of PIE root *gwa- "to go, come"). Later "act of intervening" in any way; in 19c.-20c. often of international relations; by 1983 of interpersonal intrusions by friends or family meant to reform a life felt to be going wrong.

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