'arb' originates from English, specifically as a clipped informal form of the word 'arbitrage', which itself comes from French 'arbitrage' (related to 'arbiter') and ultimately from Latin 'arbiter' meaning 'judge' or 'decider'.

'arb' developed in modern finance jargon as an abbreviation (clipping) of 'arbitrage' used by traders; 'arbitrage' entered English via French 'arbitrage' and earlier Latin 'arbiter'.

Initially a clipped shorthand for 'arbitrage', 'arb' has come to be used both as a noun meaning an arbitrage opportunity and as a verb meaning to carry out arbitrage.