Use illimitable to describe something that has no limits, like the universe, or your little brother's capacity for annoying you.

Illimitable is a rare word — and a rather fancy one. It's more common to say something's limitless or measureless, but illimitable is good if you want to sound literary or formal, say if you're talking about the "illimitable power of human endeavor." If you use illimitable to describe something like your appetite for candy, it will sound kind of funny, which is perfectly fine as long as you're going for a laugh.

Definitions of illimitable
  1. adjective
    without limits in extent or size or quantity
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