'arch-brace' is a compound of 'arch' and 'brace'. 'arch' originates from Latin, specifically the word 'arcus', where 'arcus' meant 'bow' or 'arc'; 'brace' originates from Old French 'brace' (from Latin 'bracchium'), where 'bracchium' meant 'arm' (hence a support).

'arch' entered English via Old French and Middle English from Latin 'arcus'; 'brace' came into English via Old French from Latin 'bracchium'. The compound 'arch-brace' arose in Middle English carpentry and persists in specialized architectural and woodworking vocabulary.

Initially, the components denoted 'bow/arc' and 'arm/support' respectively; over time the compound came to mean specifically an arched structural support element in frames and roof trusses.