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 ) .