Beauties oddly decrease (4)
I believe the answer is:
bate
'decrease' is the definition.
(I've seen this before)
'beauties oddly' is the wordplay.
'oddly' indicates alternate letters.
The alternating letters of 'beauties' are 'BATE'.
(Other definitions for bate that I've seen before include "Lessen" , "contention for old poet" , "decrease" , "Rage; beat the wings" .)