Secret keeping boy on toes perhaps (8)
I believe the answer is:
esoteric
'secret' is the definition.
(similar in meaning)
'boy on toes perhaps' is the wordplay.
'boy' becomes 'eric' (I've seen this before).
'on' means one lot of letters goes inside another (as in clothing 'on' a person).
'perhaps' indicates an anagram.
'toes' is an anagram of 'sote'.
'eric' placed around 'sote' is 'ESOTERIC'.
'keeping' acts as a link.
(Other definitions for esoteric that I've seen before include "Aimed at a few" , "known to a few" , "just seen by specialist" , "Understandable by only an enlightened inner circle" , "I set core up to be mysterious" .)