Nearly the end of the day? Nearly (4)
I believe the answer is:
nigh
'nearly' is the definition.
(synonyms)
'the end of the day? nearly' is the wordplay.
'the end of the day?' becomes 'night' (I've seen this before).
'nearly' means to remove the last letter.
'night' with its last letter taken off is 'NIGH'.
(Other definitions for nigh that I've seen before include "Near; close" , "Nearly" , "old touch" , "Adjacent" , "See 23" .)