Occasionally perplexed seeing weapon (4)
I believe the answer is:
epee
'weapon' is the definition.
(I know that epee is a type of sword)
'occasionally perplexed' is the wordplay.
'occasionally' indicates alternate letters (letters taken at regular intervals or occasions).
The alternate letters of 'perplexed' are 'EPEE'.
'seeing' is the link.
(Other definitions for epee that I've seen before include "Fencer's sword" , "Pointed weapon" , "Rapier" , "It may offer riposte" , "Sharp-pointed duelling sword" .)