Kind of knife with a curve, that is (5)
I believe the answer is:
bowie
'kind of knife' is the definition.
(I've seen this in another clue)
'with a curve that is' is the wordplay.
'with' is a charade indicator (letters next to each other).
'a curve' becomes 'bow' (bow is a kind of curve).
'that is' becomes 'ie' (short for Latin 'id est', 'that is').
'bow' put next to 'ie' is 'BOWIE'.
(Other definitions for bowie that I've seen before include "Rock-based chameleon" , "Art rocker David" , "David --, singer" , "Dagger-knife" , "American frontiersman, killed at the Alamo, 1836" .)