Against (preposition)

1. In opposition or hostility to.
2. In contrast or comparison with.
3. In physical contact with and exerting force on.
4. As a protection or defense against.

Origin:

Old english ongegn "opposite, in return", from on- "on" + gegn "against".

Examples:

1. He is against the idea.
2. Against the odds, he won.
3. The wall is against the window.
4. I will speak against it.
5. I have nothing against him.