'slow-released' originates from Modern English, specifically the compound of 'slow' and 'release', where 'slow' meant 'not fast' and 'release' meant 'to set free'.

'slow' derives from Old English 'slāw' meaning 'slow', while 'release' developed via Old French (e.g. 'relaisser') from Latin elements (re- + laxare/'to loosen'); these elements combined in Modern English as compounds like 'slow-release', later forming the inflected form 'slow-released'.

Initially the separate elements meant 'not fast' and 'to set free'; over time the compound came to be used especially in technical contexts (such as pharmacology) to mean 'designed to release a substance slowly', which is the modern specialized usage.