Near Rhymes:
* Component
* Exponent
* Opponent (itself, but used for emphasis)
* Moment (can work depending on context)
Eye Rhymes:
* Atonement
* Confrontment
Other Options:
* Foe (not a perfect rhyme, but works in some contexts)
* Enemy (same as above)
Ultimately, the best rhyme for "opponent" depends on the specific context and what you want to convey.