Mademoiselle is terrifying holding a spear (7)
I believe the answer is:
leister
'a spear' is the definition.
(I know that leister is a type of spear)
'mademoiselle is terrifying holding' is the wordplay.
'holding' says the answer is hidden in the clue.
'LEISTER' is hidden in the letters of 'mademoiselle is terrifying'.
(Other definitions for leister that I've seen before include "Fishing spear with three prongs" , "Pronged spear" , "Salmon-spear" , "One sticking salmon" , "long pointed object" .)