ob-2 +
(Latin: against)
Before c, ob- becomes oc-; before f, ob- becomes of-; before g, ob- becomes og-; before p, ob- becomes op-; before m, ob- becomes o-
opposite
1. Placed or located directly across from something else or from each other: opposite sides of a building.
2. Facing the other way; moving or tending away from each other: opposite directions.
3. Being the other of two complementary or mutually exclusive things.
oppress
1. To burden with cruel or unjust impositions or restraints; subject to a burdensome or harsh exercise of authority or power: "They were oppressed by totalitarianism."
2. To lie heavily upon (the mind, a person, etc.).