Expert having tendency to conceal notes (5)
I believe the answer is:
adept
'expert' is the definition.
(adept is a kind of expert)
'having tendency to conceal notes' is the wordplay.
'having tendency' becomes 'apt' ('he's apt to...' means 'he tends to...').
'to conceal' is an insertion indicator.
'notes' becomes 'de' (two musical notes).
'apt' placed around 'de' is 'ADEPT'.
(Other definitions for adept that I've seen before include "Highly proficient" , "Proficient - expert" , "One very skilled at work" , "Master" , "Very skilful, proficient" .)