Dull to get involved with (3)
I believe the answer is:
mat
'dull' is the definition.
(similar in meaning)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for mat that I've seen before include "Small rug" , "Small protective floor-covering" , "What the cat sat on?" , "Opening of good book" , "Floor-pad" .)