Long blade in swordsman's kit (3)
I believe the answer is:
ski
'long blade' is the definition.
'in swordsman's kit' is the wordplay.
'in' indicates a hidden word.
'SKI' can be found hidden inside 'swordsmans kit'.
(Other definitions for ski that I've seen before include "the end for many Russians" , "Glide or race across snow with feet attachments" , "Winter sports footwear" , "Runner for use on snow" , "Biathlon runner" .)