The poilu's hair dressing? (3)
I believe the answer is:
oil
'hair dressing?' is the definition.
The definition and answer can be both man-made objects as well as being singular nouns.
Perhaps you can see an association between them that I can't see?
'the poilu's' is the wordplay.
'OIL' is hidden within the letters.
However, I'm not sure how this is indicated.
Can you help me to learn more?
(Other definitions for oil that I've seen before include "Anoint" , "Grease" , "Black gold" , "painting" , "Viscous substance as lubricant" .)