roundhead

noun4

1. •
   A roundhead screw, one with a domed head.
2. •
   (slang) A male whose penis is circumcised.

   • The roundheads in the school showers easily equalled the cavaliers. — 1992
3. •
   Any of various agarics of the genus Stropharia.
4. •
   A circular platform at the end of a pier or breakwater.

   • The top of the caisson will be at the same level as the bag-work foundation of the pier, and a roundhead, composed of 45-ton granite faced concrete blocks, will be built on it. — 1899

adjective1

1. •
   Having a dome-shaped head.

   • The roundhead screw and its fraternal twins, the button head and pan head screws, have a head that is flat on the bottom and hemispherical on top. — 2000

noun1

1. •
   (historical) A supporter of parliament during the English Civil War (in the 17th century).