'antimoral' originates from the combining form 'anti-' (from Greek anti- 'against') plus 'moral' (from French moral, from Medieval Latin moralis).

'moral' comes from Latin 'moralis' (from 'mores' meaning 'customs' or 'manners'); the prefix 'anti-' was attached in modern English to form 'anti-moral' and later written as the single word 'antimoral' in some usages.

Initially a compound meaning 'against moral' or 'opposed to moral principles'; in modern usage it denotes either being contrary to accepted morality (immoral) or explicitly opposed to moralism as an attitude.