A continental comedian's foolish (6)
I believe the answer is:
unwise
'foolish' is the definition.
(similar in meaning)
'a continental comedian's' is the wordplay.
'a continental' becomes 'un' ('a' in French - France is on the continent).
'comedian' becomes 'wise' (I've seen this before).
'un'+'wise'='UNWISE'
(Other definitions for unwise that I've seen before include "Not sensible or prudent" , "Foolhardy" , "isn't sensible" , "Not sensible, foolish" , "Rash" .)