An unruly lock or section of hair that sticks straight out from the skull or lies at an angle at odds with the rest of an individual's hair, like a whorl or vortex.
tussock
noun
A tuft or clump of green grass or similar verdure, forming a small hillock.
How often have the words cowlick and tussock occurred in a corpus of books? (source: Google Ngram Viewer )