Long-nosed swimmer (4)
I believe the answer is:
pike
'long-nosed swimmer' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for pike that I've seen before include "Fish - medieval weapon" , "Old spear or voracious lake fish" , "Weapon on long shaft; Northern hill" , "Predator with strong teeth" , "dive in this position" .)