WordWeb Online

1. Having keenness and forcefulness and penetration in thought, expression, or intellect
   "trenchant criticism";
   - searching
    
2. Characterized by or full of force and vigour
   "a trenchant argument";
   - hard-hitting
    
3. Clearly or sharply defined to the mind
   "trenchant distinctions between right and wrong";
   - clear-cut, distinct

See also: clear, effective, effectual, efficacious, intelligent

Encyclopedia: Trenchant