Example: "Opponent (or opposing) armies"
To attempt to stop the progression of; to resist or antagonize by physical means, or by arguments, etc.; to contend against.
Example: "There is still time to oppose this plan."
To object to.
Example: "Many religious leaders oppose cloning humans."
To present or set up in opposition; to pose.
Example: "They are opposed to any form of hierarchy."
To place in front of, or over against; to set opposite; to exhibit.
That opposes or oppose; on the opposite side.
Example: "Opposing armies"