subject to individual will or judgment without restriction; contingent solely upon one's discretion

an arbitrary decision.

decided by a judge or arbiter rather than by a law or statute.

having unlimited power; uncontrolled or unrestricted by law; despotic; tyrannical

an arbitrary government.

capricious; unreasonable; unsupported

an arbitrary demand for payment.

Mathematics . undetermined; not assigned a specific value

an arbitrary constant.

arbitraries, Printing . (in Britain) peculiar ( def. 9 ) .

adjective

circumspect , rational , reasonable , reasoned , supported , democratic

adjective

approximate , capricious , discretionary , erratic , fanciful , frivolous , inconsistent , injudicious , irrational , irresponsible , offhand , optional , random , subjective , supercilious , superficial , unaccountable , unreasonable , unscientific , wayward , willful , absolute , autocratic , bossy , despotic , dogmatic , domineering , downright , flat out * , high-handed , imperious , magisterial , monocratic , no ifs ands or buts , no joke , overbearing , peremptory , straight out , summary , tyrannical , tyrannous , whimsical , judgmental , personal , absolutistic , autarchic , autarchical , autocratical , dictatorial , totalitarian , tyrannic , absolutist , arrogant , authoritarian , bigoted , captious , chance , determinate , highhanded , inexorable , positive , preferential , thetical , unrestrained