A couple, we're told, is more than you need (3)
I believe the answer is:
too
'more than you need' is the definition.
I can't tell whether this definition defines the answer.
'a couple we're told' is the wordplay.
'a couple' becomes 'two' (a couple can mean two of something).
'we're told' indicates a 'sounds like' (homophone) clue.
'two' is a homophone of 'TOO'.
'is' is the link.
Can you help me to learn more?
(Other definitions for too that I've seen before include "What a pity!" , "Excessively" , "Furthermore" , "As well, also" , "Moreover, in addition" .)