Lower area next to HQ (5)
I believe the answer is:
abase
'lower' is the definition.
(I've seen this before)
'area next to hq' is the wordplay.
'area' becomes 'a' (maths abbreviation).
'next to' says to put letters next to each other.
'hq' becomes 'base' (I've seen this before).
'a'+'base'='ABASE'
(Other definitions for abase that I've seen before include "Humble (oneself)" , "put to shame" , "Cast down" , "Demean" , "Lower" .)