Rookie acted oddly (5)
I believe the answer is:
cadet
'rookie' is the definition.
The definition and answer can be both people as well as being singular nouns.
Maybe you can see a link between them that I can't see?
'acted oddly' is the wordplay.
'oddly' indicates anagramming the letters (letters in an odd order).
'acted' is an anagram of 'CADET'.
Can you help me to learn more?
(Other definitions for cadet that I've seen before include "Young trainee, eg in the police" , "junior role" , "Police force trainee" , "not the heir" , "Younger member of family" .)