The object is to get a spare key (5)

I believe the answer is:

thing

I'm a little stuck... Click here to teach me more about this clue!

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

'a spare key' is the wordplay.
'a spare' becomes 'thin' (I've seen this in another clue).
'key' becomes 'g' (musical key).
'thin'+'g'='THING'

'get' acts as a link.

Can you help me to learn more?

(Other definitions for thing that I've seen before include "cup of tea" , "An unnamed object or item" , "Inanimate object" , "Body" , "Night (anag)" .)

I've seen this clue in the Evening Standard.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.