helmet

noun

1. a protective covering for the head; specif.,
   1. the headpiece of ancient or medieval armor
   2. the metal head covering worn in modern warfare
   3. the rigid head covering with inner padding and often a wire face mask used in football, lacrosse, and hockey
   4. the mesh-faced mask used in fencing
   5. the headpiece of a diver's suit, equipped with air tubes, glass windows, etc.
   6. a fireman's protective hat
   7. a pith hat with a wide brim, worn as a sunshade in hot countries
   8. the rigid head covering worn by a motorcyclist
   9. hard hat
2. something suggesting such a headpiece in appearance or function, as a galea of a flower

transitive verb