Criminal in jail but keeping old feeling of joy (10)
I believe the answer is:
jubilation
'feeling of joy' is the definition.
(jubilation is a joyful feeling)
'criminal in jail but keeping old' is the wordplay.
'criminal' indicates anagramming the letters.
'keeping' means one lot of letters goes inside another.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'in'+'jail'+'but'='injailbut'
'injailbut' anagrammed gives 'jubilatin'.
'jubilatin' enclosing 'o' is 'JUBILATION'.
(Other definitions for jubilation that I've seen before include "Joy" , "Triumphal rejoicing" .)