'intellection' originates from Latin, specifically the word 'intellectio' (seen also as the accusative 'intellectionem'), where the root 'intelligere' meant 'to understand' (from 'inter-' "among" + 'legere' "to pick/read").

'intellection' changed from Late Latin 'intellectio' and passed through Medieval/Scholastic Latin (and influence from Old French/Anglo-Norman usage in scholarly contexts) before entering Middle/Modern English as 'intellection'.

Initially, it meant 'the act or faculty of understanding', and over time it has largely retained that sense while also being used to denote 'a particular thought or conception' produced by the intellect.