unreasonably rigid in the face of argument or entreaty or attack
She squirmed, wanting him inside her right now, but either he wasn’t cooperating or she was too clumsy to angle them into the right position, which, she rued, given her inexperience, was possible. But it doesn’t seem that he’s being particularly helpful, she thought mulishly, breaking their kiss long enough to look at him. His silvery gaze was wicked…and cockily amused.
Moning, Karen Marie (2008-05-20). Kiss of the Highlander (Kindle Locations 1997-1999). Random House, Inc.. Kindle Edition.
Definition pasted from: <http://www.onelook.com/?w=mulish&ls=a>