Name in heading dead stupid, reason kept secret (6,6)
I believe the answer is:
hidden agenda
'reason kept secret' is the definition.
'hidden agenda' can be an answer for 'reason' (I have seen 'Undisclosed reason' mean 'hidden agenda' so perhaps 'reason' could also mean 'hidden agenda'). I'm not certain of the 'kept secret' bit.
'name in heading dead stupid' is the wordplay.
'name' becomes 'n' (common abbreviation e.g. on forms).
'in' means one lot of letters goes inside another.
'stupid' indicates anagramming the letters (in a stupid order).
'heading'+'dead'='headingdead'
'headingdead' is an anagram of 'hiddeagenda'.
'n' inserted within 'hiddeagenda' is 'HIDDEN AGENDA'.
Can you help me to learn more?
(Other definitions for hidden agenda that I've seen before include "covert plan" , "Sub-text, unstated objective" , "Secret motive behind one's actions" , "Undisclosed reason" , "Ulterior motive" .)