He can be catty (3)

I believe the answer is:
tom
'he' is the definition.
(I've seen this in another clue)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for tom that I've seen before include "famous schoolboy" , "Cruise" , "Male feline" , "type pursuing queen" , "Boy - cat" .)
