End of scarf covered by moist part of cloth (4)
I believe the answer is:
weft
'part of cloth' is the definition.
(threads used when making cloth)
'end of scarf covered by moist' is the wordplay.
'end of' says to take the final letters.
'covered by' means one lot of letters goes inside another.
'moist' becomes 'wet' (similar in meaning).
The final letter of 'scarf' is 'f'.
'f' inserted inside 'wet' is 'WEFT'.
(Other definitions for weft that I've seen before include "crossing line served by a shuttle?" , "Yarn woven across the warp" , "Threads woven into and crossing the warp" , "Strands (carried across by shuttle)" , "What is threaded across warp" .)