c. 1600, "attending, incidental," also "derived from circumstances," from Latin circumstantia (see circumstance) + -al (1). Related: Circumstantially. Legalese circumstantial evidence "evidence from more or less relevant circumstances bearing upon a case," as distinguished from direct testimony, is attested by 1691.
"state of mind which results from satisfaction with present circumstances," 1570s, from content (adj.). Phrase heart's content is from 1590s (Shakespeare).