Mother tours Australia with extremely reticent musical composer (6)
I believe the answer is:
mozart
'musical composer' is the definition.
'mozart' can be an answer for 'composer' (Mozart is an example). I also know that 'musical' relates to this answer.
'mother tours australia with extremely reticent' is the wordplay.
'mother' becomes 'ma' (ma is a kind of mother).
'tours' means one lot of letters goes inside another.
'australia' becomes 'oz'.
'with' says to put letters next to each other.
'extremely' says to hollow out the word (remove centre letters).
'reticent' with its centre removed is 'rt'.
'ma' enclosing 'oz' is 'moza'.
'moza'+'rt'='MOZART'
(Other definitions for mozart that I've seen before include "Composer of Don Giovanni, d. 1791" , "Wolfgang Amadeus . . . . . . 18th century Austrian composer" , "'Cosi fan tutte' composer" , "The composer can be found in an OZ mart" , "Magic Flute composer" .)