Note odd piece in sword (4)
I believe the answer is:
epee
'sword' is the definition.
(sword used in fencing)
'note odd piece' is the wordplay.
'note' becomes 'e' (musical note).
'odd' indicates alternate letters.
The alternate letters of 'piece' are 'pee'.
'e'+'pee'='EPEE'
'in' acts as a link.
(Other definitions for epee that I've seen before include "It may offer riposte" , "Narrow fencing sword" , "Pointed weapon" , "Fencer's sword" , "there's a point to it" .)