ONCE, at once; for good and all; used also for additional emphasis.
ONLY, pre-eminent, special.
OPEN, make public; expound.
OPPILATION, obstruction.
OPPONE, oppose.
OPPOSITE, antagonist.
OPPRESS, suppress.
ORIGINOUS, native.
ORT, remnant, scrap.
OUT, "to be—," to have forgotten one's part; not at one with each other.