OBNOXIOUS, liable, exposed; offensive.
OBSERVANCE, homage, devoted service.
OBSERVANT, attentive, obsequious.
OBSERVE, show deference, respect.
OBSERVER, one who shows deference, or waits upon another.
OBSTANCY, legal phrase, "juridical opposition."
OBSTREPEROUS, clamorous, vociferous.
OBSTUPEFACT, stupefied.
ODLING, (?) "must have some relation to tricking and cheating" (Nares).
OMINOUS, deadly, fatal.