Cardinal shut a don out (8)
I believe the answer is:
thousand
'cardinal' is the definition.
(similar in meaning)
'shut a don out' is the wordplay.
'out' is an anagram indicator (out can mean wrong or inaccurate).
'shut'+'a'+'don'='shutadon'
'shutadon' anagrammed gives 'THOUSAND'.
(Other definitions for thousand that I've seen before include "cube" , "Figure" , "See 1 down" , "Numeric value of kilo" , "M or K" .)