Nearly all (4)
I believe the answer is:
most
'nearly all' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for most that I've seen before include "Nearly all, majority" , "In the highest degree" , "Greatest in amount or degree" , "Extremely, very" , "Kind of commercial pact where two countries agree to treat each other as well as any other" .)