One held Munro to be windy -- crackpot mountaineered ignoring that (8)
I believe the answer is:
detainee
'crackpot mountaineered ignoring that' is the definition.
The definition and answer can be both people as well as being singular nouns.
Perhaps you can see a link between them that I can't see?
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for detainee that I've seen before include "One penned" , "Prisoner" , "Person kept in custody" , "One is held under guard, for political reasons perhaps" , "Someone held in custody" .)