The term 'THICK HEAD OF HAIR' can be summarized by two crossword solutions: MANE (4 letters) and MOP (3 letters). A MANE is a thick, long growth of hair on the head of an animal, usually referring to horses. In humans, a MANE is a term used to describe a thick head of hair. A MOP is a tool used for cleaning floors, but it can also refer to a person's head of hair, usually when it is thick and unruly. Therefore, the term 'THICK HEAD OF HAIR' can be summarized as a long, thick growth of hair on the head, or a thick, unruly head of hair.