Immensity (4)
![Ross](/clue/static/ross-mug.min.png)
I believe the answer is:
bulk
'immensity' is the definition.
(thesaurus)
This is all the clue.
(Other definitions for bulk that I've seen before include "Size - mass" , "Majority" , "Large mass; roughage" , "Greater part" , "Mass of something large" .)