'right-angled' originates from English compounding: specifically the words 'right' + 'angle' with the adjectival suffix '-ed'.

'angle' originates from Latin, specifically the word 'angulus' where it meant 'corner'; it passed into Old French as 'angle' and into English. 'right' comes from Old English 'riht' meaning 'straight' or 'correct'. These elements were later combined in English to form the compound adjective 'right-angled'.

Initially the components meant 'straight/correct' and 'corner' respectively; their combination came to mean 'having a 90° corner' and this meaning has remained stable.