Calculator in a taxi returned by you and me (6)
I believe the answer is:
abacus
'calculator' is the definition.
(abacus is a kind of calculator)
'a taxi returned by you and me' is the wordplay.
'taxi' becomes 'cab' (synonyms).
'returned' says the letters should be written backwards.
'by' means one lot of letters go next to another.
'you and me' becomes 'us' (the two of us).
'cab' reversed gives 'bac'.
'a'+'bac'+'us'='ABACUS'
'in' acts as a link.
(Other definitions for abacus that I've seen before include "Basic calculator makes" , "As a cub (anag)" , "one counts on it" , "Totter" , "calculator needed" .)