Substance (5)
'substance' is the definition.
(I know that stuff is a type of substance)
This is all the clue.
(Other definitions for stuff that I've seen before include "Substance; material" , "set with unspecified ingredients" , "Material - things" , "Cram; material" , "crowd" .)
'substance' is the definition.
(synonyms)
This is the entire clue.
(Other definitions for matter that I've seen before include "Substance as opposed to spirit" , "Physicist giving name to frequency shift" , "Physical substance" , "No . . . . . . - it is unimportant" , "See 18" .)
'substance' is the definition.
(both can mean something's essence or gist)
This is the entire clue.
(Other definitions for pith that I've seen before include "Spongy tissue lining rinds of oranges, or the essential part" , "Citrus rind lining" , "Tissue inside the rind of citrus fruits" , "Inside skin of, say, orange" , "Core - essence" .)