0
The opposite of ad infinitum would be concise.
The mathematical area of a circle is a measurement that repeats itself ad infinitum.
The number system continues ad infinitum.
opposite of ad infinitum is finite, as in there is a limit.
We continued walking through the woods ad infinitum, never reaching the end of the dense forest.
Ad infinitum the boy punches his pillow with rage.
Impossible to answer - since you're specifying 'ad infinitum' which means 'to infinity'.