n. 1  1. A form of a verb in some languages, such as Classical Greek, that expresses action without indicating its completion or continuation. 2  2. A form of a verb in some languages, such as Classical Greek or Sanskrit, that in the indicative mood expresses past action. [From Greek aoristos, indefinite, aorist tense : a-, not; see a-1 + horistos, definable (from horizein, to define; see horizon).]