woolly-headed

Adjective

 * : having tightly curled and frizzy hair.
 * 1) * 1708 Feb 25, The British Apollo:
 * The Blacks in Guinea are Woolly-headed.
 * : characterized by vague or confused thinking, dull-witted.

Usage notes
As an insult, although present use is generally understood as an allusion to having a head full of wool, the original racist supposed connection between hair similar to wool and intelligence can make this and similar terms offensive.

Synonyms

 * See Thesaurus:foolish & Thesaurus:stupid