Oddly missing sleazier den (4)
I believe the answer is:
lair
'den' is the definition.
(I know that den can be written as lair)
'oddly missing sleazier' is the wordplay.
'oddly missing' means one should take alternating letters (letters in odd-numbered positions removed).
The alternating letters of 'sleazier' are 'LAIR'.
(Other definitions for lair that I've seen before include "Rail around animal's den" , "Wild animal's retreat" , "Animal's resting place" , "Habitation of a wild animal" , "Secret base" .)