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a. A protective head covering made of hard material, such as leather, metal, or plastic: A firefighter's uniform includes a helmet.
b. The headgear with a glass mask worn by deep-sea divers.
c. A pith helmet; a topi.
d. A head covering, such as a balaclava, that is shaped like a helmet.
2. A piece of armor, usually made of metal, designed to protect the head.
3. Botany The hood-shaped sepal or corolla of some flowers.
tr. & intr.v. hel·met·ed, hel·met·ing, hel·mets
To provide with or put on a helmet.
[Middle English, from Old French, diminutive of helme, of Germanic origin; see kel- in Indo-European roots.]
adj → behelmt