Preventer \Pre*vent"er\, n. 1. One who goes before; one who forestalls or anticipates another. [Obs.] --Bacon. 2. One who prevents or obstructs; a hinderer; that which hinders; as, a preventer of evils or of disease. 3. (Naut.) An auxiliary rope to strengthen a mast. {Preventer bolts}, or {Preventer plates} (Naut.), fixtures connected with preventers to re["e]nforce other rigging. {Preventer stay}. (Naut.) Same as {Preventer}, 3.