Stiffness adjectives are listed in this post. Each word below can often be found in front of the noun stiffness in the same sentence. This reference page can help answer the question what are some adjectives commonly used for describing STIFFNESS.
arterial, certain, elastic, formal, great
greater, high, higher, joint, lateral
less, little, low, mechanical, military
more, much, muscle, muscular, necessary
neck, relative, same, slight, sufficient
Hope this word list had the adjective used with stiffness you were looking for. Additional describing words / adjectives that describe / adjectives of various nouns can be found in the other pages on this website.