Conservationists engaging a certain ensemble (5)
I believe the answer is:
nonet
'certain ensemble' is the definition.
The definition suggests a singular noun which matches the answer.
'conservationists engaging a' is the wordplay.
'conservationists' becomes 'NT' (abbreviation for National Trust).
'engaging' means one lot of letters goes inside another (inserted letters are engaged or involved in others).
'a' becomes 'one'.
'nt' placed around 'one' is 'NONET'.
Can you help me to learn more?
(Other definitions for nonet that I've seen before include "Band of nine?" , "Instrumental group of nine players" , "Tonne (anag.); music for a group" , "Group of nine musicians" , "group composition" .)