'arcus' originates from Latin, specifically the word 'arcus', where the root 'arc-' meant 'bow' or 'arch'.

'arcus' passed from Classical Latin into Medieval/Neo-Latin scientific usage as 'arcus' and was later adopted into English in technical contexts (anatomy, meteorology) as 'arcus' (plural 'arcuses').

Initially it meant 'bow' or 'arch' in a general sense; over time it became specialized to mean anatomical arches and arch-like cloud formations in modern usage.