Do you know ghouls from goblins and ghosts?
c.1500, from Middle French sagacité, from Latin sagacitatem (nominative sagacitas) "keenness of perception, quality of being acute," from sagax (genitive sagacis) "of quick perception, acute," related to sagus "prophetic," sagire "perceive keenly," from PIE root *sag- "to track down, trace, seek" (cf. Old English secan "to seek;" see seek). Also used 17c.-18c. of animals, meaning "acute sense of smell."