O interj. An exclamation used in calling or directly addressing a person or personified object; also, as an emotional or impassioned exclamation expressing pain, grief, surprise, desire, fear, etc.
    For ever, O Lord, thy word is settled in heaven.   --Ps. cxix. 89.
    O how love I thy law ! it is my meditation all the day.   --Ps. cxix. 97.
 Note: ☞ O is frequently followed by an ellipsis and that, an in expressing a wish: “O [I wish] that Ishmael might live before thee!” --Gen. xvii. 18; or in expressions of surprise, indignation, or regret: “O [it is sad] that such eyes should e'er meet other object!”
 Note: ☞ A distinction between the use of O and oh is insisted upon by some, namely, that O should be used only in direct address to a person or personified object, and should never be followed by the exclamation point, while Oh (or oh) should be used in exclamations where no direct appeal or address to an object is made, and may be followed by the exclamation point or not, according to the nature or construction of the sentence. Some insist that oh should be used only as an interjection expressing strong feeling.  The form O, however, is, it seems, the one most commonly employed for both uses by modern writers and correctors for the press. “O, I am slain!” --Shak. “O what a fair and ministering angel!” “O sweet angel !” --Longfellow.
    O for a kindling touch from that pure flame!   --Wordsworth.
 But she is in her grave, -- and oh
 The difference to me!   --Wordsworth.
    Oh for a lodge in some vast wilderness!   --Cowper.
    We should distinguish between the sign of the vocative and the emotional interjection, writing O for the former, and oh for the latter.   --Earle.
 O dear, ∧ O dear me! , exclamations expressive of various emotions, but usually promoted by surprise, consternation, grief, pain, etc.
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