'antimelancholic' originates from combining elements in Greek and modern English: the prefix 'anti-' (from Greek anti-, meaning 'against') attached to 'melancholic' (from Greek 'melankholia').

'melancholic' comes from Greek 'melankholia' (melan- 'black' + khole 'bile'), passed into Latin as 'melancholia' and into Middle English as 'melancholy/melancholic'; 'anti-' from Greek combined with the modern English adjective to form the compound 'antimelancholic' in more recent English coinage.

Initially the Greek root related to the physiological notion of 'black bile' associated with sadness; over time the sense shifted to psychological sadness ('melancholy'), and 'antimelancholic' has come to mean 'against or countering that sadness.'