Almost, well-nigh (6)
I believe the answer is:
nearly
This clue is a double definition.
'almost' is the first definition.
(I know that almost can be written as nearly)
'well-nigh' is the second definition.
(synonyms)
(Other definitions for nearly that I've seen before include "Not entirely" , "approximately" , "Close" , "More or less" , "Almost, well-nigh" .)