American organisation referred to in pleasant retrospective (4)
I believe the answer is:
nasa
'american organisation' is the definition.
The definition suggests a singular noun which matches the answer.
'referred to in pleasant retrospective' is the wordplay.
'referred to in' says the answer is hidden in the clue.
'retrospective' says the letters should be written in reverse.
'asan' is hidden in the letters of 'pleasant'.
'asan' back-to-front is 'NASA'.
Can you help me to learn more?
(Other definitions for nasa that I've seen before include "US headquarters for space exploration" , "rocket launcher" , "US agency responsible for space flight" .)