French friends set out in poor visibility (3,4)
I believe the answer is:
sea mist
'poor visibility' is the definition.
The definition suggests a singular noun which matches the answer.
'french friends set out' is the wordplay.
'french friends' becomes 'amis' (I've seen this in another clue).
'out' is an insertion indicator.
'amis' put inside 'set' is 'SEA MIST'.
'in' is the link.
Can you help me to learn more?
(Another definition for sea mist that I've seen is " The 'haar' of eastern England and Scotland coasts, for example".)