Small mound (7)
'small mound' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for hillock that I've seen before include "elevated ground" , "it requires little effort to get up" , "Rising" , "Mound, knoll" , "Barrow" .)
(Other definitions for tuffet that I've seen before include "Little Miss Muffet sat on hers" , "Where arachnophobe sat" , "Miss Muffet's seat" .)