(Gr. νύμφαι, Lat. nymphae), in Greek and Roman mythology, a class of inferior female deities of almost infinite number, who were held to preside over all parts of the earth. They were commonly represented as beautiful young women, and generally in the train of some of the greater divinities, such as Neptune, Juno, Diana, or Pan. In most parts of Greece and Italy they were worshipped with offerings of kids, lambs, milk, or honey, but never of wine. In the latter country they were sometimes honoured with special temples or chapels. The interest they took in men and human affairs was believed to be entirely of a kindly and beneficent nature. They presided alike over the dry land and the watery element. In the former class the most important were the mountain nymphs, the Orcodes or Orodemniades, who also took local names from the special hills which they haunted, such as Citharonides, &c.; the nymphs of trees, the Dryades and Hamadryades, whose life was commensurate with that of the forest tree in which they had their abode; and the nymphs of valleys and groves, the Nopaze, &c. Of the water-nymphs the most important were the Oceanides, the daughters of Oceanus and Tethys, said to be 3000 in number. After them may be named the Nereids, the daughters of Nereus and Doris, fifty in number, of whom the most famous were Amphitrite, the wife of Neptune; Thetis, the mother of Achilles; Galatea, &c. Their favourite haunt was the Ægean Sea, and they were held in high honour throughout Greece, especially at Corinth. The river-nymphs, the Potameides, were worshipped under local names, derived from the special rivers over which they presided; such as Acheloïdes, from the Achelous; Pactolides, from the Pactolus, &c. The Naiades, or nymphs of the fresh water, were known as Limnaeides and Creneae, or Pegae, according as they inhabited lakes or springs. Even the waters of Hades had their presiding nymphs, the Avernades, many of whom were believed to be endowed with prophetic power, and to communicate that gift to their favourites among men. O, the fifteenth letter and the fourth vowel of the English alphabet, occupies a position in point of sound between the vowels a and u. The shape of the letter seems to have originated in the circular form assumed by the lips in pronouncing it; yet in the hieroglyphical characters, and even in the ancient Greek alphabet, it appears to have been taken from the shape of the eye. In English O has a long sound, as in bone, moan, broke, roll, which is usually denoted in a word or syllable by a final e, as in bone, lonely, or by a servile a as in moan, roaming. It has also a short sound as in hot, long, and a soft sound like the Italian u and the French ou, as in move, which is shortened in words ending in a close articulation, and represented by oo as in look, root. The vowel o is convertible with a variety of vowels and of vowel combinations, in English, as well as in other languages; e.g., what is o to the eye is u to the ear in the words son, none, done, won. The English o in the words one, two, gone becomes a in Scotch as one, two, gane; and o interchanges with ea in cleave, clove; heat, hot, &c. O was used as a numeral by the ancients to represent 11, and with a dash over it (O) to denote 11,000. Among the Irish O prefixed to proper names, like Fitz in England and Mac in Scotland, signifies son of, as O'Neal, the son of Neal; and was originally employed as a character of family dignity. O, a circle, or CQ is called by the Italians circolo, and is used by them to express tempo perfetto in music, or what we call triple time. (For the use of O in abbreviations, see ABBREVIATIONS.) O is often employed as an interjection to express a wish, admiration, pity, surprise, &c.; but when strong emotion is to be conveyed, the exclamation is written Oh!