Deepest (6)
I believe the answer is:
inmost
'deepest' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for inmost that I've seen before include "Furthest inward" , "Furthest inwards, closest to centre" , "Monist (anag.)" , "Being deepest within the self" , "Situated or occurring farthest within" .)