Crazy unknown has some (4)
I believe the answer is:
zany
'crazy' is the definition.
(I've seen this in another clue)
'unknown has some' is the wordplay.
'unknown' becomes 'z' (algebra).
'has' means one lot of letters go next to another.
'some' becomes 'any' (similar in meaning).
'z'+'any'='ZANY'
(Other definitions for zany that I've seen before include "Absurd" , "Clownish; wacky" , "Like a buffoon" , "Mad" , "Madcap, like a clown" .)