Possibly omits when wet (5)
I believe the answer is:
moist
'wet' is the definition.
(I know that wet can be written as moist)
'possibly omits' is the wordplay.
'possibly' is an anagram indicator.
'omits' is an anagram of 'MOIST'.
'when' acts as a link.
(Other definitions for moist that I've seen before include "Affected by tears, perhaps" , "bit wet" , "Dampish" , "Damp, humid" , "sloppy" .)