'postmolt' originates from the Latin prefix 'post-' and the English word 'molt'; 'post-' meant 'after' and 'molt' meant 'to shed (feathers, skin, or an exoskeleton).

'postmolt' was formed in modern scientific English by combining the Latin prefix 'post-' with the existing English verb/noun 'molt'. The noun/verb 'molt' appears in Middle English (often as forms related to 'mouten'/'moult') and later stabilized into the modern English forms 'moult' (UK) and 'molt' (US).

Initially, 'molt' referred specifically to the act of shedding; when combined with 'post-' the compound has meant 'after shedding' since its formation and retains that biological sense today.