Resentment shown when a futile plan has gone astray (7)
I believe the answer is:
dudgeon
'resentment' is the definition.
(I've seen this before)
'has gone astray' is the wordplay.
'has' becomes 'dud' (I am not sure about this - if you are sure you should believe this answer much more).
'astray' is an anagram indicator.
'gone' anagrammed gives 'geon'.
'dud'+'geon'='DUDGEON'
'shown when a futile plan' acts as a link.
This may not be correct. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for dudgeon that I've seen before include "Deep resentment" , "Feeling of intense indignation" , "State of being (highly) aggrieved" , "(High) resentment" , "Anger" .)