One of the unpaid trainees? Bury has any number (6)
I believe the answer is:
intern
'one of the unpaid trainees?' is the definition.
'bury has any number' is the wordplay.
'bury' becomes 'inter' ('inter' can be a synonym of 'bury').
'has' says to put letters next to each other.
'any number' becomes 'n' (I've seen this in other clues).
'inter'+'n'='INTERN'
(Other definitions for intern that I've seen before include "Hold in custody" , "Hospital doctor (US)" , "Confine as a prisoner" , "Novice gaining experience" , "Imprison without trial - hospital junior doctor" .)