THE fourth letter in the Phoenician system of writing, and in most of those derived from it. It is the representative of the last four classes into which the sounds of human speech may be divided; A representing the first or faucal (vocal) class, B the second or labial, and C the third or guttural. The letters of this fourth, denti-lingual or lingui-dental class, viz., d, t, s, z, l, r, are visible signs of the articulated sounds produced by various movements of the tongue 'touching the teeth and gums, and are therefore convertible into each other; and from a misunderstanding of the real character of human phonetism, and of its graphic representation, the combination th, and even g, j, and ch, have been and are used instead of the letters of the fourth class. D is the sonorous counterpart of T, and is produced by applying the tip of the tongue to the superior incisive teeth and to their gum, while the tongue, obliquely rising, obstructs the passage of the breath; then by suddenly withdrawing this obstruction, while the larynx resounds (oscillates) during the passage of the air through the glottis, the sound in question is exploded.

When the larynx does not thus resound, we utter the harder T. The Z, r, are strictly lingui-dental, and d, t, s, z, denti-lingual. The Semitic name daleth (whence the Greek delta), signifying door, gate, has nothing to do either with the nature of the sound or with the figure of the letter, and was probably chosen merely on account of its beginning with this sound. Its figure is more or less triangular, and more or less rounded, while in many so-called alphabets it is a mere angle or crook. In old Slavic it occupies (erroneously) the 5th place, in Ethiopic the 19th, or, counting the Amharic additions, the 24th. Its hieroglyphs are the segment of a circle, an open hand, a beetle, which designate both T and D. Moreau de Dammartin derives the figure from the northern triangle, and from the little triangle in the head of the ram in the zodiac. In Arabic there are four modifications of it, to wit: dal (4, as a numeral sign), the 8th letter; dzal (700), the 9th; dhad (800), the 15th; and dha (900), the 17th; but in Cufic writing only the first is used. The Devanagari has two series of letters, each consisting of five (t, th, d, dh, n), one of which is named cerebral or lingual, and the other dental; most of the modes of writing employed in the middle and south of Asia follow this arrangement.

In Mongolic and Mantchooric D is distinguished from T by a dot, as it is also in the runes. The Finns, Lapps, and other northern people, scarcely distinguish it from T. It is the only sonorous consonant with the Hurons, and was very prevalent among the natives of the Mexican plateau and in the Quichua of South America. It does not occur on Etruscan monuments, T being used in its place. Grimm exhibits the convertibility of the lingui-dentals as follows:

This scheme is illustrated in some of the following examples:

Gr. Goth, dauhtar, old Ger. Tochtar, Eng. daughter." Gr. Goth, tunhthus, old Ger. Zant, Eng. tooth, etc. Latin: quodannis and quotonnis; tendo, tensum; prehendo, prehensum. Euphonic: proves, , French gendre, etc, instead of pro-es, av-pες, gen-re, etc. Walla-chian, eece, Lat. decern; si, dies; ore, hordeum. Ital. TVa-pani, Lat. Drepana. D is ejected from the following: Ital. aombrare, Lat. adumbrare; Po, Lat. Padus, etc.; Span, oir, caer, creer, Lat. audire, cadere, credere; so in the French, outr, Juif, sueur, Lat. audire, Judaeus, sudor. L substituted for D: cicada, Lat. cicada; Span. cola, Lat. cauda; Portug. juZgar, Lat. judicare; Ulysses, Zacryma, , etc. R substituted for D: meridies for medidies. D is lost in the following: Ital. a,pie, Lat. ad, pede, etc.; Span.fe, Lat. fides. Ger. Theil, deal; gut, good; Gott, God; Blut, blood, etc. Ital. danzare, French danser, Ger. tansen, Lat. ten-dere. Ital. Aldobrando, Ger. Alt-brandt; Tancredo, Dank-rath, etc. Eng. ten, tooth, token; Lat. decern, dens, docu-mentum; Ger. sehn, sahn, seichen, etc. Ger. dick, thick.; dunn, thin; Daum, thumb; der, die, das, the. Lat. participle passive, -atom, -itum; Eng. -ed; Span, -ado, -ido, etc.

D began to be used as a numeral sign for 500 about A. D. 1500, when the Dutch printers employed the 10 in the ancient CIO (M), 1,000, combining those signs in the figure of D. It was used by the Romans in the following abbreviations: D. for Decius, Dominus, Divus, Deus, Dictator, Dacia, Diges-tum, etc.; D. D. for De-cemvirorum decreto; D. D. D. for Decernvirorum decreto datum, also for Dat, donat, dedicat; d. for die, dabam (I wrote), etc.; D. M., Diis mani-bus; D. O. M., Deo op-timo maximo. With the Catholics D is the dominical letter when the first Sunday in January falls on the 4th. - On the reverse of European coins D indicates Lyons in France, Au-rich and Diisseldorf in Prussia, and Gratz in Austria. - D in music denotes the second interval of the present German and English diatonic scale, or the third string of the chromatic scale; this was the re of Guido Aretino, and is the la of the French.