H is found in fifteen consecutive letters in code (5)
I believe the answer is:
ethos
'code' is the definition.
(moral code)
'h is found in fifteen consecutive letters' is the wordplay.
'is found in' means one lot of letters goes inside another.
'fifteen consecutive letters' becomes 'E to S'.
'h' inserted into 'etos' is 'ETHOS'.
'in' is the link.
(Other definitions for ethos that I've seen before include "Pervading spirit" , "Underlying culture of a group" , "Characteristic spirit (of, eg, a culture)" , "moral code" , "Philosophy" .)