'aptitude-based' is a compound formed from 'aptitude' + 'based'. 'Aptitude' originates from Latin 'aptitudo' via French 'aptitude', where Latin 'aptus' meant 'fit' or 'suitable'. 'Based' comes from 'base', which derives from Latin 'basis' through Old French 'base'.

'aptitude' passed from Latin 'aptitudo' into French and then into English as 'aptitude'; 'base' came from Latin 'basis' to Old French 'base' and into Middle English as 'base'. The compound construction using 'based' (as in 'X-based' meaning 'founded on X') developed in modern English by combining nouns with 'based' to form adjectives.

Individually, 'aptitude' originally meant 'fitness' or 'suitability' and 'base' meant a foundation. Over time, the compound 'aptitude-based' came to specifically mean 'founded on or determined by aptitude' in contexts like selection, training, or placement.