Old cat incredibly precise (5)
I believe the answer is:
exact
'precise' is the definition.
(synonyms)
'old cat incredibly' is the wordplay.
'old' becomes 'ex' (prefix meaning former or onetime).
'incredibly' is an anagram indicator.
'cat' anagrammed gives 'act'.
'ex'+'act'='EXACT'
(Other definitions for exact that I've seen before include "Particular" , "Strict" , "As a right, demand" , "Not approximate; inflict (revenge) on someone" , "Precise and strictly correct" .)