arb

The word 'arb' is a modern financial slang term, a clipped form of 'arbitrageur'. An arbitrageur is someone who practices arbitrage, which is the simultaneous buying and selling of securities, currency, or commodities in different markets to profit from price discrepancies. The term 'arbitrage' itself entered English from French in the late 18th century, derived from the Old French 'arbitrage', meaning 'judgment' or 'arbitration', which in turn comes from the Latin 'arbitrari', meaning 'to judge' or 'to give a decision'. Thus, the journey is from the concept of a judge making a decision to a trader making a calculated financial decision to exploit market imbalances.

This is a clipped form, a back-formation from the longer word 'arbitrageur'. It is not composed of classical morphemes in its current, abbreviated state.