Couple keeping strangely hush about Charlie's baby carriage (9)
I believe the answer is:
pushchair
'baby carriage' is the definition.
(synonyms)
'couple keeping strangely hush about charlie's' is the wordplay.
'couple' becomes 'pair' (synonyms).
'keeping' is an insertion indicator (some letters kept inside).
'strangely' indicates anagramming the letters.
'about' is a charade indicator (letters next to each other).
'charlie' becomes 'C' (phonetic alphabet: alpha, bravo, charlie etc.).
'hush' after 'c' is 'chush'.
'chush' with letters rearranged gives 'ushch'.
'pair' enclosing 'ushch' is 'PUSHCHAIR'.
(Other definitions for pushchair that I've seen before include "Baby transport" , "Baby mover" , "transport for youngster" .)