Taboo  (also tabu) —n. (pl. -s) 1 ritual isolation of a person or thing as sacred or accursed. 2 prohibition imposed by social custom. —adj. Avoided or prohibited, esp. By social custom (taboo words). —v. (-oos, -ooed or -us, -ued) 1 put under taboo. 2 exclude or prohibit, esp. Socially. [tongan]