Something to start singing on key (4)

I believe the answer is:

song

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'something to' is the definition.
I can't tell whether this defines the answer.

'start singing on key' is the wordplay.
'start' suggests taking the first letters.
'key' becomes 'g' (musical key).
The initial letter of 'singing' is 's'.
's'+'on'+'g'='SONG'

Can you help me to learn more?

(Other definitions for song that I've seen before include "Carol, for instance" , "Unnecessary fuss" , "Musical rendition" , "Tune" , "Melody (which is cheap to go for)" .)

I've seen this clue in the Evening Standard.

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