'post-collapse' is formed from the prefix 'post-' (from Latin 'post', meaning 'after') attached to the noun 'collapse' (from Latin 'collapsus', from 'collabi' meaning 'to fall together').

'post-' entered English via Latin and Old French as a productive prefix meaning 'after'; 'collapse' entered English from Latin 'collapsus' (past participle of 'collabi') in the early modern period; the two elements have been combined in contemporary English to form the compound 'post-collapse' to describe the time or conditions following a collapse.

Initially the parts meant 'after' ('post-') and 'to fall together' ('collapse'); when combined they originally described simply 'after a collapse', and the modern usage retains that basic sense while often implying enduring social, economic, or infrastructural consequences.