DALETH. The fourth letter in the Heb. alphabet (ד), originally shaped like a triangle with no projecting leg at the right-hand corner (such as characterized the letter rēsh) until the 7th century b.c. and thereafter (when it became more easily confused with (ר), rēsh, even though the latter normally had a longer tail projecting from its lower right angle). Later on, when “square Heb.” characters developed (apparently in Aram. circles during the 6th cent.), daleth assumed the shape of an up-side-down “L” (with the short horizontal arm projecting leftward); oddly enough, rēsh also assumed a similar shape (ר), except that the angle corner was somewhat rounded, and never developed a tittle (or projection to the right of the vertical stroke) as daleth did. This letter was pronounced d as in Eng., although in later times it spirantized to the th sound in the Eng. “this” when it was preceded by a vowel sound. As a numerical sign, daleth represented the number four.

International Standard Bible Encyclopedia (1915)

The 4th letter of the Hebrew alphabet, and as such used in Ps 119 to designate the 4th section; transliterated in this Encyclopedia with the dagesh as d, and, without, as dh ( = th in "the"). It came also to be used for the number four (4), and with the dieresis for 4,000. With the apostrophe it is sometimes used as abbreviation for the tetragrammaton. For name, etc., see Alphabet.