Girl beginning to tire carrying home musical instrument (8)
I believe the answer is:
clarinet
'musical instrument' is the definition.
(I know that clarinet is a clarinet)
'girl beginning to tire carrying home' is the wordplay.
'girl' becomes 'clare' ().
'beginning to' says to take the initial letters.
'carrying' indicates putting letters inside.
'home' becomes 'in' ('he's home' can mean 'he's in').
The first letter of 'tire' is 't'.
'clare'+'t'='claret'
'claret' going around 'in' is 'CLARINET'.
(Other definitions for clarinet that I've seen before include "Find an instrument in claret" , "Wind instrument made from Clare tin" , "Woodwind instrument played by Artie Shaw and Benny Goodman" , "Music maker" , "that works off wind" .)