'arbitrative' originates from Latin, specifically from the noun 'arbiter' (judge, witness) and the verb 'arbiterari' (to judge, to give an opinion).

'arbiter' passed into Old French as 'arbiteur/arbiter' and into Middle English in forms such as 'arbitre'/'arbitrer'; from the verb 'arbitrate' (to settle by arbitration) the adjective form 'arbitrative' developed in modern English to describe things relating to arbitration.

Initially related to a judge or one who gives an opinion ('arbiter' as judge/witness), over time the sense specialized to formal processes of settling disputes and now means 'relating to arbitration' or 'acting as an arbitrator'.