Crossword Genius

Measure a spare part (3)

Ross

I believe the answer is:

are

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

'measure' is the definition.
(are is a kind of measure)

'a spare part' is the wordplay.
'spare part' becomes 're' (re is a kind of part. I am not sure about the 'spare' bit.).
'a'+'re'='ARE'

Can you help me to learn more?

(Other definitions for are that I've seen before include "Is, in the plural" , "Era (anag.)" , "(We/you/they) exist" , "is for more than one" , "live" .)

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