'anticlimax' originates from Greek, specifically the word 'antiklimax' (ἀντικλίμαξ), where the prefix 'anti-' meant 'against' or 'opposite' and 'klimax' meant 'ladder' or 'staircase' (by extension 'climax' or 'summit').

'anticlimax' entered English via New Latin and French in the late 16th to 17th centuries; the Greek compound passed into Latin/French forms and then into Modern English as 'anticlimax', keeping the sense of a downward step from an expected summit.

Initially it referred to a rhetorical descent (a step down from a prior level of importance), but over time it came to be used more broadly for any disappointing or less intense conclusion (the modern sense of 'a letdown').