Tom's broken nearly all (4)
I believe the answer is:
most
'nearly all' is the definition.
(I've seen this in another clue)
'tom's broken' is the wordplay.
'broken' indicates an anagram.
'toms' is an anagram of 'MOST'.
(Other definitions for most that I've seen before include "Greatest in amount or degree" , "Nearly all, majority" , "Extremely, very" , "Kind of commercial pact where two countries agree to treat each other as well as any other" , "Almost all" .)