Success pitilessly stymies one full of crap (7)
I believe the answer is:
cesspit
'crap' is the definition.
Although both the answer and definition are singular nouns, I cannot understand how one could define the other.
'success pitilessly stymies one full of' is the wordplay.
'one full of' says the answer is hidden in the clue (inside).
'CESSPIT' is hidden within 'success pitilessly stymies'.
Can you help me to learn more?
(Other definitions for cesspit that I've seen before include "Foul and squalid place" , "means of waste disposal" , "Place for filthy water" , "Sewage holder" , "Sump" .)