'Coochy-coo' etc: additional vacuous expressions embraced by yours truly (9)
I believe the answer is:
motherese
'coochy-coo etc' is the definition.
(language used when talking to babies)
'additional vacuous expressions embraced by yours truly' is the wordplay.
'additional' becomes 'other' (other or additional things).
'vacuous' suggests removing the centre.
'embraced by' means one lot of letters goes inside another.
'yours truly' becomes 'me' (the person who set this crossword).
'expressions' with its middle taken out is 'es'.
'other'+'es'='otheres'
'otheres' placed into 'me' is 'MOTHERESE'.
(Another definition for motherese that I've seen is " baby talk".)