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-
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-