Enormous number hunt missing adult big cat (8)

I believe the answer is:
trillion
'enormous number' is the definition.
(I've seen this in another clue)
'hunt missing adult big cat' is the wordplay.
I cannot quite understand how this works, but
'adult' could be 'lion' (lion is a kind of adult) and 'lion' is found within the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for trillion that I've seen before include "enormous figure" , "Very large number" , "US billion" , "A great number" , "1 and 18 zeros" .)
