hang-dog (adj.)

1794, "recklessly daring person, one who fears nothing and will attempt anything," from dare (v.) + devil (n.). The devil might refer to the person, or the sense might be "one who dares the devil." For the formation, compare scarecrow, killjoy, dreadnought, pickpocket (n.), cut-throat, also fear-babe a 16c. word for "something that frightens children;" kill-devil "bad rum," sell-soul "one who sells his soul" (1670s).

As an adjective, "characteristic of a daredevil, reckless," by 1832. Related: Daredevilism; daredeviltry.