Drain ground, lowest point (5)
I believe the answer is:
nadir
'lowest point' is the definition.
(I've seen this before)
'drain ground' is the wordplay.
'ground' is an anagram indicator ('grind' the letters into a new form).
'drain' with letters rearranged gives 'NADIR'.
(Other definitions for nadir that I've seen before include "Low point" , "Low-water mark" , "businessman formerly escaping justice" , "It's the depths" , "Floor of drain in need of repair" .)