Value but throw out (5)
I believe the answer is:
worth
'value' is the definition.
(I've seen this before)
'throw out' is the wordplay.
'out' indicates an anagram (out can mean wrong or inaccurate).
'throw' is an anagram of 'WORTH'.
'but' is the link.
(Other definitions for worth that I've seen before include "Value (of something)" , "Throw (anag.)" , "Merit - value" .)