nudism n.

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.

word-forming element making nouns implying a practice, system, doctrine, etc., from French -isme or directly from Latin -isma, -ismus (source also of Italian, Spanish -ismo, Dutch, German -ismus), from Greek -ismos, noun ending signifying the practice or teaching of a thing, from the stem of verbs in -izein, a verb-forming element denoting the doing of the noun or adjective to which it is attached. For distinction of use, see -ity. The related Greek suffix -isma(t)- affects some forms.

1929, adjective and noun, from French nudiste or formed in English from nude (adj.) + -ist; see nudism.