Tide type (4)
I believe the answer is:
neap
'tide type' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for neap that I've seen before include "The half-way kind of tide" , "Least in difference between high and low tides" , "Tide of smallest rise and fall" , "Tide when there is the least variation between high and low water" , "Tide of minimum range" .)