Obligative mode, [90] (footnote).
Observance, confused with observation, [195].
Obsolete words, [185-186].
Of, Glossary.
Omission, of adverb much, [45]; of important words, [127] (5); of prepositions, [108]; punctuation in case of [140] (§117); [143] (§138); of verbs, [87].
One another, use of, [40].
Only, placing of, [41]; with a negative, [42], Glossary.
Order of heading in letters, [155-156].
Other, use of in comparison, [37].
Ought, [50].