Noun-making suffix
I believe the answer is:
ness
'noun-making suffix' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for ness that I've seen before include "Loch of monster fame" , "Headland, promontory" , "Loch in the Great Glen" , "Scottish lake with traditional monster" , "Eliot -, led effort against Al Capone; Scots loch" .)