You'll find one in a monastery garden (5)
I believe the answer is:
aster
'you'll' is the definition.
Both the definition and answer are singular nouns.
Maybe there's an association between them I don't understand?
'one in a monastery garden' is the wordplay.
'one in' indicates a hidden word.
'ASTER' can be found hidden inside 'monastery garden'.
'find' is the link.
Can you help me to learn more?
(Other definitions for aster that I've seen before include "bloomer" , "Michaelmas daisy genus" , "Garden plant" , "Showy garden flower" , "Daisy-like garden flower" .)