Group of soldiers or policemen crossing river (5)
I believe the answer is:
corps
'group of soldiers' is the definition.
(I've seen this before)
'policemen crossing river' is the wordplay.
I cannot really see how this works, but
'river' could be 'r' (abbreviation) and 'r' is found within the answer.
'policemen' could be 'cops' (cop is a kind of policeman) and 'cops' is found within the remaining letters.
This accounts for all the letters.
This explanation may well be incorrect...
'or' is the link.
Can you help me to learn more?
(Other definitions for corps that I've seen before include "Army grouping" , "army band" , "ballet group" , "Body of men" , "Group of soldiers" .)