Use permeating fluid? (10)
I believe the answer is:
impregnate
'use' is the definition.
Although both the answer and definition are verbs in their base form, I can't understand how they can define each other.
'permeating fluid?' is the wordplay.
'fluid?' indicates anagramming the letters (I've seen 'fluid' mean this).
'permeating' is an anagram of 'IMPREGNATE'.
(Other definitions for impregnate that I've seen before include "Saturate with a substance" , "Saturate - permeating (anag)" , "soak" , "Fill" , "Infuse" .)