More unyielding is a term that describes something that is very difficult to change or influence. The crossword solutions for this term are 'sterner' (7 letters), 'harder' (6 letters), and 'stonier' (7 letters). All three words describe something that is more difficult to alter or move than usual, with sterner referring to a more serious attitude, harder referring to a greater degree of difficulty, and stonier referring to something that is more solid and immovable.