'post-dawn' is a modern English compound formed from the prefix 'post-' and the noun 'dawn'. The prefix 'post-' comes from Latin 'post' meaning 'after', and 'dawn' is the modern English word for the time of day when light first appears.

'post-' entered English via Latin (and Old French influence) as a productive combining form meaning 'after'; 'dawn' comes from Old English 'dagian'/'dawnian' (related to Proto-Germanic *dagaz 'day') and developed into Middle English 'dawn' before becoming the modern word 'dawn'. The compound 'post-dawn' is a descriptive formation in Modern English combining those elements.

Initially the elements meant 'after' (post-) and 'the coming of day' (dawn); together in modern usage they simply denote timing 'after dawn' with little additional figurative shift.