Unknown faces, arse-covering (1-6)
I believe the answer is:
y-fronts
'arse-covering' is the definition.
I know nothing about this answer so I cannot judge whether this works.
'unknown faces' is the wordplay.
I cannot really understand how this works, but
'unknown' could be 'y' (algebra) and 'y' is found in the answer.
'faces' could be 'fronts' (fronting is a kind of facing) and 'fronts' is found within the answer.
This accounts for all the letters.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for y-fronts that I've seen before include "Male undergarment" , "Men's underwear" , "briefs" , "Style of underpants" , "Pants for men" .)