Bottom of well covered by moist leather strip (4)
I believe the answer is:
welt
'leather strip' is the definition.
(part of a shoe)
'bottom of well covered by moist' is the wordplay.
'bottom of' suggests the final letters.
'covered by' means one lot of letters goes inside another.
'moist' becomes 'wet' (similar in meaning).
The final letter of 'well' is 'l'.
'l' inserted within 'wet' is 'WELT'.
(Other definitions for welt that I've seen before include "Fire(place)" , "After blow, Mark" , "narrow ridge" , "High Ottoman official" , "Wound from lash" .)