Note about old dry mound (5)
I believe the answer is:
motte
'mound' is the definition.
Both the definition and answer are singular nouns.
Maybe they are linked in a way I don't understand?
'note about old dry' is the wordplay.
'note' becomes 'me' (musical note as in do-re-me).
'about' indicates putting letters inside.
'old' becomes 'o' (abbreviation).
'dry' becomes 'tt' (abbreviation for teetotal).
'o'+'tt'='ott'
'me' enclosing 'ott' is 'MOTTE'.
Can you help me to learn more?
(Other definitions for motte that I've seen before include "Rise in defence" , "Tumulus" , "Castle mound" .)