Large farm animal nearly joins donkey tripping over through ha-ha (8)

I believe the answer is:
colossal
'large' is the definition.
(similar in meaning)
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for colossal that I've seen before include "Mammoth" , "Huge, immense" , "Enormous, gigantic" , "Stupendous" , "Giant" .)
