1. (prep.) Abreast; opposite to; facing; towards; as, against the mouth of a river; -- in this sense often preceded by over.

2. (prep.) From an opposite direction so as to strike or come in contact with; in contact with; upon; as, hail beats against the roof.

3. (prep.) In opposition to, whether the opposition is of sentiment or of action; on the other side; counter to; in contrariety to; hence, adverse to; as, against reason; against law; to run a race against time.

4. (prep.) By of before the time that; in preparation for; so as to be ready for the time when.