Airmen rerouted river for seaman (7)
I believe the answer is:
mariner
'seaman' is the definition.
(I know that seaman can be written as mariner)
'airmen rerouted river' is the wordplay.
'rerouted' indicates anagramming the letters (I've seen this in other clues).
'river' becomes 'r' (abbreviation for river).
'airmen' anagrammed gives 'marine'.
'marine'+'r'='MARINER'
'for' acts as a link.
(Other definitions for mariner that I've seen before include "Bluejacket" , "See 13" , "Sea dog" , "Seafarer, old salt" , "Probe" .)