Passage that accommodates retreating soldiers (6)
I believe the answer is:
throat
'passage' is the definition.
(throat is a kind of passage)
'that accommodates retreating soldiers' is the wordplay.
'accommodates' is an insertion indicator.
'retreating' says the letters should be written in reverse.
'soldiers' becomes 'or' (Other Rank).
'or' reversed gives 'ro'.
'that' placed around 'ro' is 'THROAT'.
(Other definitions for throat that I've seen before include "end of gaff" , "Gorge - frog's location?" , "Passage from the back of the mouth" , "It's inside the neck" , "Where the gullet and windpipe are located" .)