'prolonged-release' is a modern English compound formed from 'prolonged' and 'release'. 'Prolonged' ultimately derives from Latin 'prolongare' (from 'pro-' meaning 'forward' and 'longus' meaning 'long'), and 'release' comes via Old French (e.g. 'relaisser'/'relivre') from Latin roots related to loosening (e.g. 'relaxare').

'prolonged' comes from Latin 'prolongare' → Middle French/Old French influences → Middle English 'prolongen'/'prolonged' and developed into modern English 'prolonged'; 'release' passed from Latin into Old French (forms like 'relaisser') and then into Middle English as 'release', eventually forming the compound modern English term 'prolonged-release' in pharmaceutical contexts in the 20th century.

Individually, 'prolong' originally meant 'to make long or extend'; 'release' originally meant 'to loosen or set free'. Combined in modern usage they specifically denote formulations that 'extend the period over which an active substance is released' (a technical pharmaceutical meaning that developed with controlled/extended drug-delivery technology).