THE fourteenth letter and fourth vowel of our alphabet, being pronounced as in the words rose, hose. The sound of this letter is often so soft as to require it double, and that chiefly in the middle of words, as goose, reproof, woof; and in some words this double oo is pronounced like u short, as in blood, flood. As a numeral, O was sometimes used for 11 amongst the ancients, and with a dash over it, thus, O, it stood for 11,000. In the notes of the ancients, O CON. is read opus conductum; O C Q. opera constilique; O D M. opere donum munus; and O LO. opus locution. The Greeks had two O's, namely, the omikron, ω, and the omega, ω; the one being pronounced on the tip of the lips with a sharper sound, and the other in the middle of the mouth, with a fuller sound, equal to oo in our language. The long and short pronunciations of our O are equivalent to the two Greek ones. O is usually denoted as long by a servile a subjoined, as moan; or by e at the end of the syllable, as bone; but when these vowels are not used it is generally short. Amongst the Irish, the letter O, at the beginning of the name of a family, is a character of dignity annexed to great houses. Thus, in the history of Ireland, we frequently meet with the O'Neals, O'Carrolls, and O'Connells, considerable personages in that island. Indeed Campden observes, that it is the custom of the lords of Ireland to prefix an O to their names, to distinguish them from the commonalty. The ancients used O as a mark of triple time, from a notion that the ternary, or number 3, was the most perfect of numbers, and therefore properly expressed by a circle, which is the most perfect of figures. It is not, strictly speaking, the letter O, but the figure of a circle O, or double CO, by which the early moderns used to express in music what they called tempo perfetto, or triple time; and hence the Italians call it circolo. The seven antiphones, or alternate hymns of seven verses, sung by the choir in the time of Advent, were formerly called O, from their beginning with such an exclamation.

O, or Oh, is an adverb of calling, or interjection of sorrow or wishing.