Lower, under (6)
I believe the answer is:
nether
I believe this clue is a double definition.
'lower' is the first definition.
(as in nether regions)
'under' is the second definition.
(synonyms)
(Other definitions for nether that I've seen before include "Subordinate" , "inferior" , "These garments are for the bottom half" , "These regions are hell, the underworld" , "Lower, like regions or garments" .)