Enterprise to air by river (7)
I believe the answer is:
venture
'enterprise' is the definition.
(I've seen this before)
'air by river' is the wordplay.
'air' becomes 'vent' (both can mean to express or reveal).
'by' says to put letters next to each other.
'river' becomes 'ure' (River Ure).
'vent'+'ure'='VENTURE'
'to' acts as a link.
(Other definitions for venture that I've seen before include "Commercial undertaking that risks a loss but promises a profit" , "The undertaking involves uncertainty" , "Put at risk" , "Uncertain undertaking" , "Dare to put forward" .)