'rectangularity' originates from English, specifically the adjective 'rectangular' + the noun-forming suffix '-ity' (from French '-ité' and Latin '-itas').

'rectangular' developed from Latin elements 'rectus' meaning 'right' and 'angulus' meaning 'angle' (via Medieval/ Late Latin 'rectangulus'), entered English as 'rectangular', and 'rectangularity' was later formed by adding '-ity' to denote the state or quality.

Initially connected to the idea of 'right-angled' or 'having right angles,' it evolved into the nominal sense 'the state or quality of being rectangular.'