'anti-moralistic' is a compound formed from the Greek prefix 'anti-' (from ἀντί) meaning 'against' and 'moralistic', which derives from 'moral' (from Latin 'moralis' < 'mos, moris' meaning 'custom') plus the suffix '-istic' (via Greek/Latin/French) indicating relating to an ideology or practice.

'moral' entered English via Old French from Latin 'moralis' (from 'mos, moris' meaning 'custom'); the adjective 'moralistic' was formed in English by adding the productive suffix '-istic'. The combining form 'anti-' has been used in English since borrowing from Greek to create compounds meaning 'against', leading to formations like 'anti-moralistic'.

Initially the parts referred to being 'against custom' (anti-) and to matters of 'custom or morals' (moral); together as 'anti-moralistic' the term came to mean specifically 'opposed to moralizing attitudes' rather than a literal opposition to all customs.