The Oxford Thesaurus An A-Z Dictionary of Synonyms - arbitrary adj.

1) capricious, varying, erratic, uncertain, inconsistent, doubtful, unpredictable, whimsical, irrational, chance, random, inconsistent, subjective, unreasoned, irrational, Colloq chancy, iffy: The choices are entirely arbitrary, totally at the whim of the council and not based on research or knowledge. 2) absolute, tyrannical, despotic, authoritarian, magisterial, summary, peremptory, autocratic, dogmatic, imperious, uncompromising, inconsiderate, high-handed, dictatorial, Rare thetic(al) : The conduct of the archbishop appears to have been arbitrary and harsh.