Some pretty neat river (4)
I believe the answer is:
tyne
'river' is the definition.
(I've seen this before)
'some pretty neat' is the wordplay.
'some' indicates a hidden word (some of the parts of the word are used).
'TYNE' is hidden in the letters of 'pretty neat'.
(Other definitions for tyne that I've seen before include "Serve as evidence for" , "River running through Newcastle" , "Northumbrian river" , "Gateshead's river" , "River of Northumberland" .)