leitmotiv, n. [G., leading motive.].
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a guiding theme; in Wagnerian opera, a marked melodic phrase or short musical passage which always accompanies the reappearance of a certain person, situation, abstract idea, or allusion in the course of the play; a sort of musical label. Also called Leading motive. [1913 Webster]
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a recurring theme in the activities of a person or group. [PJC]