Vessel too short for waterways (6)
I believe the answer is:
canals
'waterways' is the definition.
(I know this)
'vessel too short' is the wordplay.
'vessel' becomes 'can' (type of container).
'too' becomes 'also' (synonyms).
'short' means to remove the last letter.
'also' with its last letter taken away is 'als'.
'can'+'als'='CANALS'
'for' is the link.
(Other definitions for canals that I've seen before include "Man-made waterways" , "Artificial water channels" , "Artificial waterways" .)