WAW. This sixth letter of the Heb. alphabet, written in Square Heb. as a vertical stroke with a leftward hook at the top (ו), went back to an epigraphic form resembling a capital “Y” with short diagonals and a long vertical tail. This in turn seems, on the basis of the Sinaitic inscrs. from Serabit el-Khadim, to have represented a battle mace (a short wooden staff with a pear-shaped stone head fastened on one end of it) of the type frequently represented in Egyp. bas-reliefs of the Pharaohs. The letter was anciently pronounced like Eng. w; in later times it acquired a sound more like v (hence it is often called vav rather than waw), which prevails in Israeli pronounciation at the present time. As a number the waw represented 6.
International Standard Bible Encyclopedia (1915)
"w": The sixth letter of the Hebrew alphabet; transliterated in this Encyclopedia "w" (or "v"). It came also to be used for the number 6. For name, etc., see Alphabet.