'single-core' is a compound formed in modern English from 'single' and 'core'. 'single' ultimately derives from Latin 'singulus' (via Old French), meaning 'one, single', and 'core' comes from Old English 'cor' (from Latin 'cor') meaning 'heart' or 'central part'.

'single' comes from Latin 'singulus' → Old French (via medieval usage) → Middle English 'single'. 'core' originally meant 'heart' in Old English and later extended to mean the central or most important part; in the 20th century 'core' gained the technical sense of a CPU execution unit, and the compound 'single-core' arose in computing jargon to specify processors with one such unit.

Individually, 'single' meant 'one' and 'core' meant 'heart' or 'central part'; over time 'core' acquired a technical meaning in computing ('processing core'), so 'single-core' came to mean 'having one processing core' specifically in computing contexts.