My cougar is running wild (8)
I believe the answer is:
gracious
'my' is the definition.
(both are exclamations of surprise)
'cougar is running wild' is the wordplay.
'running wild' indicates an anagram.
'cougar'+'is'='cougaris'
'cougaris' anagrammed gives 'GRACIOUS'.
(Other definitions for gracious that I've seen before include "Well-mannered" , "Gosh" , "Elegant - polite" , "Affable, courteous, kindly" , "Showing qualities associated with good taste and manners" .)