Lion's share (4)
'lion's share' 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" , "Extremely, very" , "Kind of commercial pact where two countries agree to treat each other as well as any other" , "Greatest in amount or degree" .)
(Other definitions for bulk that I've seen before include "Mass (eg for buying)" , "Large mass; roughage" , "Amplitude" , "Volume or size" , "Size - mass" .)