An Infinite Word™...

Has a single closed capital letter (e.g. A, O, P, etc.) in its left half and one in its right half, with the center letter of odd-lettered words not being one.

An Infinite Word™...

has a single capital letter with a closed region (e.g. A, D, O, P, Q, or R) in its left half and one in its right half, with the center letter of odd-lettered words not being one of those. This bears similarity to an infinity symbol, where there is a closed region on each side (hence the name Infinite Word™, I presume).

There is one undefined condition: it's unclear from the examples above how to consider the letter B, since it has two closed regions. The only word with a B is OBLIVIOUS, which is already disqualified as an Infinite Word™ because it has an O on the right and a OB on the left. If a letter B is treated just like any other letter with a closed region then, for example, BIGOT would be an Infinite Word™.