Story one cadet concocted (8)
I believe the answer is:
anecdote
'story' is the definition.
(thesaurus)
'one cadet concocted' is the wordplay.
'concocted' indicates an anagram.
'one'+'cadet'='onecadet'
'onecadet' with letters rearranged gives 'ANECDOTE'.
(Other definitions for anecdote that I've seen before include "Short entertaining story" , "Pithy account of an incident" , "Neat code (anag.)" , "Humorous story" , "Yarn" .)