1530s, a legal term, "unsupported, not formally attested," from Latin nudus "naked, bare, unclothed, stripped," from PIE root *nogw- "naked" (see naked). General sense of "mere, plain, simple" is attested from 1550s. In reference to the human body, "unclothed, undraped," it is an artistic euphemism for naked, dating from 1610s (implied in nudity) but not in common use in this sense until mid-19c.
"the representation of the undraped human figure in visual art," 1708, from French nud, obsolete variant of nu "naked, nude, bare," from Latin nudus (see nude (adj.)). In the nude "in a condition of being unclothed" is by 1856.