Strengthen with something soft (3)
I believe the answer is:
wax
'strengthen' is the definition.
(thesaurus)
'with something soft' is the wordplay.
I cannot really see how this works, but
'with' could be 'w' (abbreviation) and 'w' is located in the answer.
The remaining letters 'ax' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for wax that I've seen before include "Increase in strength or size, like ear matter" , "Increase (as moon's phase)" , "Grow large" , "increase like stuff in ears" , "Increase in phase (as moon)" .)