lacking in harmony between the different parts or elements; self-contradictory

an inconsistent story.

lacking agreement, as one thing with another or two or more things in relation to each other; at variance

a summary that is inconsistent with the previously stated facts.

not consistent in principles, conduct, etc.

He's so inconsistent we never know if he'll be kind or cruel.

acting at variance with professed principles.

Logic . incompatible ( def. 4b ) .

adjective

consistent , consonant , regular , steady , unchanging

adjective

at odds , at variance , capricious , changeable , conflicting , contrary , discordant , discrepant , dissonant , erratic , fickle , illogical , incoherent , incompatible , in conflict , incongruent , incongruous , inconstant , irreconcilable , lubricious , mercurial , out of step , temperamental , uncertain , unpredictable , unstable , variable , warring , patchy , spotty , unsteady , fantastic , fantastical , freakish , ticklish , volatile , whimsical , antagonistic , contradictory , disagreeing , divergent , immiscible , inharmonious , irregular , paradoxical , repugnant , uncongenial