Shorten a river crossing? (7)
I believe the answer is:
abridge
'shorten' is the definition.
(synonyms)
'a river crossing?' is the wordplay.
'river crossing?' becomes 'bridge'.
'a'+'bridge'='ABRIDGE'
(Other definitions for abridge that I've seen before include "Edit down" , "prune?" , "(US) cattle-pen" , "Make shorter, book say" , "Shorten written work" .)