Someone unwilling to change is said to be “as ________ as a mule”

Answer of Word Craze Someone unwilling to change is said to be as as a mule

This is a tricky question of Word Craze which last appeared on Level 426. Meanings or answers can change from time to time with each game update if you noticed a change on the answer of this clue please do let us know by commenting below so we can fix it A.S.A.P.
The solution below is:

For other clue answers of Level 426 Word Craze Level 426 Answer open the the level link.