Arrangements one may be reduced to (5)
I believe the answer is:
ranks
'arrangements' is the definition.
(rank is a kind of arrangement)
'one may be reduced to' is the wordplay.
I cannot really understand how this works, but
'one' could be 'an' (an apple is one apple) and 'an' is found within the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for ranks that I've seen before include "Series of soldiers" , "Grades, in armed forces say" , "Rows (of soldiers)" , "Classifies" , "Lines or rows of people or things" .)