Wife sandwiched between vacuous Toronto couple (3)
I believe the answer is:
two
'couple' is the definition.
(two people or things)
'wife sandwiched between vacuous toronto' is the wordplay.
'wife' becomes 'w'.
'sandwiched between' indicates putting letters inside.
'vacuous' says to hollow out the word (remove centre letters).
'toronto' with its middle removed is 'to'.
'w' placed into 'to' is 'TWO'.
(Other definitions for two that I've seen before include "not very many" , "Pair; hour after lunch" , "II" , "Cat's coat" , "Company, so it's said" .)