Lower or upper regions adjacent to Pole (6)
I believe the answer is:
nether
'lower' is the definition.
(as in nether regions)
'upper regions adjacent to pole' is the wordplay.
'upper regions' becomes 'ether' (I've seen this in another clue).
'adjacent to' is a charade indicator (letters next to each other).
'pole' becomes 'n' (abbreviation for North, as in North Pole).
'ether' after 'n' is 'NETHER'.
'or' is the link.
(Other definitions for nether that I've seen before include "Lower in position" , "Lower, like regions or garments" , "Located below" , "inferior" , "Situated below" .)