Kind of tide (4)
I believe the answer is:
neap
'kind of tide' is the definition.
(I know that neap is a type of high tide)
This is the entire clue.
(Other definitions for neap that I've seen before include "Small tide" , "Tide with the smallest vertical range" , "Tide with least fall and rise of water" , "It's between spring and ebb" , "The middle-sized tide" .)