The majority are stray toms (4)
I believe the answer is:
most
'the majority' is the definition.
(most of a group)
'stray toms' is the wordplay.
'stray' indicates an anagram.
'toms' is an anagram of 'MOST'.
'are' is the link.
(Other definitions for most that I've seen before include "In the highest degree" , "Almost all" , "Extremely, very" , "Nearly all, majority" , "Kind of commercial pact where two countries agree to treat each other as well as any other" .)