Minimum-range tide (4)
I believe the answer is:
neap
'minimum-range tide' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for neap that I've seen before include "Tide when there is the least variation between high and low water" , "A less than average tide" , "Tide of smallest rise and fall" , "The middle-sized tide" , "Tide with least fall and rise of water" .)