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1. Based on or subject to individual discretion or preference or sometimes impulse or caprice
   "an arbitrary decision"; "the arbitrary rule of a dictator"; "an arbitrary penalty"; "of arbitrary size and shape"; "an arbitrary choice"; "arbitrary division of the group into halves"
    
2. (technical) having any value or form, of any degree or extent
   "an arbitrary function"

See also: absolute, arbitrariness, capricious, discretional, discretionary, impulsive, whimsical

Antonym: nonarbitrary

Encyclopedia: Arbitrary Arbitrary, capricious and unreasonable