Cadet Jan might be very close (8)
I believe the answer is:
adjacent
'very close' is the definition.
(I've seen this before)
'cadet jan might be' is the wordplay.
'might be' is an anagram indicator.
'cadet'+'jan'='cadetjan'
'cadetjan' anagrammed gives 'ADJACENT'.
(Other definitions for adjacent that I've seen before include "Close by" , "Contiguous" , "Alongside" , "Nearby" , "Next-door" .)