Sailor in river, airmen flying over (7)
I believe the answer is:
mariner
'sailor' is the definition.
(mariner means a sailor)
'river airmen flying over' is the wordplay.
'river' becomes 'r' (abbreviation).
'flying' is an anagram indicator (letters fly around into new positions).
'over' means one lot of letters goes inside another.
'airmen' with letters rearranged gives 'mainer'.
'r' inserted into 'mainer' is 'MARINER'.
'in' is the link.
(Other definitions for mariner that I've seen before include "Person sailing" , "Seafarer, old salt" , "Sea dog" , "Man of the sea" , "Probe" .)