O - (Webster's 1828 Dictionary)
O is the fifteenth letter, and the fourth vowel in the English Alphabet. The shape of this letter seems to have been taken from the circular configuration of the lips in uttering the sound. It corresponds in figure with the Coptic O, and nearly with the Syriac initial and final vau, and the Ethiopic ain. In words derived from the oriental languages, it often represents the vau of those languages, and sometimes the ain; the original sound of the latter being formed deep in the throat, and with a greater aperture of the mouth.
In English, O has a long sound, as in tone, hone, groan, cloke, roll, droll; a short sound, as in lot plod, rod, song, lodge. The sound of oo is shortened in words ending in a close articulation, as in book and foot.
The long sound of O, is usually denoted by e, at the end of a word or syllable, as in bone, lonely; or by a servile a, as in moan, foal. It is generally long before ll, as in roll; but it is short in doll, loll, and in words of more syllables than one, as in folly, volley.
As a numeral, O was sometimes used by the ancients for 11, and with a dash over it for 11,000.
Among the ancients, O was a mark of tripe time, from the notion that the ternary or number 3, is the most perfect of numbers, and properly expressed by a circle, the most perfect figure.
O is often used as an exclamation, expressing a wish.
O, were he present.
It sometimes expresses surprise. Shakespeare uses O for a circle or oval.
Within this wooden O.
O.S. stands for Old Style.