Wood perhaps flattening itself (3-4)
I believe the answer is:
non-iron
'wood' is the definition.
Both the answer and definition are adjectives.
Perhaps you can see an association between them that I can't see?
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for non-iron that I've seen before include "Like easy-care clothes" , "Like wrinkle-free materials" , "Type of material (probably also drip-dry)" , "(Of fabric) easy care" .)