Bits of skeleton a tailless dog buried in good faith (4,5)
I believe the answer is:
bona fides
'good faith' is the definition.
(I've seen this before)
'bits of skeleton a tailless dog buried in' is the wordplay.
'bits of skeleton' becomes 'bones' (I can't justify this - if you can you should believe this answer much more).
'tailless' means to remove the last letter (the tail of the word is removed).
'dog' becomes 'fido' (I've seen this before).
'buried in' means one lot of letters goes inside another (inserted letters get buried).
'fido' with its last letter removed is 'fid'.
'a'+'fid'='afid'
'bones' placed around 'afid' is 'BONA FIDES'.
Can you help me to learn more?
(Other definitions for bona fides that I've seen before include "Honesty and sincerity of intention" , "In good faith (Latin)" .)