Nearly everything thus as well (4)
I believe the answer is:
also
'as well' is the definition.
('also' can be a synonym of 'as well')
'nearly everything thus' is the wordplay.
'nearly' means to remove the last letter.
'everything' becomes 'all' (I've seen this before).
'thus' becomes 'so' ('so' can be a synonym of 'thus').
'all' with its final letter taken off is 'al'.
'al'+'so'='ALSO'
(Other definitions for also that I've seen before include "To boot" , "Furthermore" , "revolutionary a part for Yugoslavia" , "Plus" , "As well, in addition" .)