Men on bunk, one turning round (5)
I believe the answer is:
rotor
'one turning round' is the definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Maybe there's a link between them I don't understand?
'men on bunk' is the wordplay.
'men' becomes 'OR' (military abbreviation for Other Ranks).
'on' means one lot of letters go next to another.
'bunk' becomes 'rot' (synonyms).
'or' put after 'rot' is 'ROTOR'.
Can you help me to learn more?
(Other definitions for rotor that I've seen before include "Revolving bar" , "Revolving blade (as on helicopter)" , "Palindromic moving part" , "Turning part of machine, palindromic" , "Part of electric motor" .)