Note: Do not rely on this information. It is very old.
SS, the 19th letter in the English alphabet, and the last one but one in the Phoenician, from which it passed to the Greek. It has a sharp hissing sound, which is sometimes represented by ss or e, and the soft sound also, represented by z. As the teeth and tongue are both employed in its production, it is classed sometimes as a dental, sometimes as a lingual, and is also called a semi-vowel. In German it is generally soft at the beginning of a word, and hard at the middle or end, the English use being, for the most part, the reverse of this. Many Latin words with initial s in passing into French acquired the prefix e, as spatium, espace; and the s is often dropped entirely, e.g. thalatta for thalassa, etc., and in many cases the lisping th is substituted for s. Some South Sea islanders are unable to pronounce s.