hang out (v.)youdaoicibaDictYouDict[hang out 词源字典]
c. 1400, intransitive (as of the tongue, from the mouth); transitive use by 1560s; see hang (v.) + out (adv.). Colloquial meaning "to be found" is recorded from 1811, "in allusion to the custom of hanging out a sign or 'shingle' to indicate one's shop and business" [Century Dictionary]. As a noun (often hangout) "residence, lodging" attested from 1893; earlier "a feast" (1852, American English).[hang out etymology, hang out origin, 英语词源]