Entry 1 sense Webster, 1913 Stiffener /stĭf'-ən-ẽr/ · Stiff·en·er · IPA /stˈɪfənər/ 01 n. One who, or that which, stiffens anything, as a piece of stiff cloth in a cravat. 1. One who, or that which, stiffens anything, as a piece of stiff cloth in a cravat.