a member or supporter of the Parliamentary, or Puritan, party in England during the English civil war (1642-52): originally a derisive term, with reference to the Puritans' close-cropped hair in contrast to the Cavaliers' long hair
See Roundhead in American Heritage Dictionary 4
noun
A supporter of the Parliamentarians during the English Civil War and the Commonwealth.
Origin:
Origin: From the close-cropped hair of the Puritans