A Helmet

1. A protective head covering, usually part of armour.
2. That which resembles a helmet in form, position, etc.

• The upper part of a chemist's retort.
• The hood-shaped upper sepal or petal of some flowers, as of the monkshood or the snapdragon.
• A naked shield or protuberance on the top or fore part of the head of a bird.
• (heraldry) The feature above a shield on a coat of arms.
• The glans penis.

brain bucket, hard hat