No, "biggest" is not a noun. It is the superlative form of the adjective "big."
A Siberian Tiger is the biggest big cat
The adjective 'biggest' is the superlative form for the adjective 'big': big, bigger, biggest
big
The biggest "big" cat is the Siberian Tiger.
New Zealands biggest rock is a beach rock they can be as big as a big big super big mountin
the world's biggest mythical creature is pretty big
Biggest - Big Star album - was created in 1994.
BIG Asia is the biggest continent. It has 18.8 million square miles.
really big
BIG
Big Big