arbitrary
1 capricious, chance, discretionary, erratic, fanciful, inconsistent, optional, personal, random, subjective, unreasonable, whimsical, wilful
2 absolute, autocratic, despotic, dictatorial, dogmatic, domineering, high-handed, imperious, magisterial, overbearing, peremptory, summary, tyrannical, tyrannous, uncontrolled, unlimited, unrestrained
Antonyms
1 consistent, judicious, logical, objective, rational, reasonable, reasoned, sensible, sound