Ouse winding across English county, lastly, is so long (3,3)
I believe the answer is:
see you
'is so long' is the definition.
(I've seen this in another clue)
'ouse winding across english county lastly' is the wordplay.
'winding' is an anagram indicator.
'across' means one lot of letters goes inside another.
'english' becomes 'E' (abbreviation as in OED).
'lastly' indicates one should take the final letters.
The final letter of 'county' is 'y'.
'ouse' with letters rearranged gives 'seou'.
'e'+'y'='ey'
'seou' going around 'ey' is 'SEE YOU'.
(Other definitions for see you that I've seen before include "Casual and informal goodbye" , "Later we'll meet" , "Informal kind of au revoir - with visual intent" , "Bye!" , "Cheers" .)