The spelling of the word "Sithe" might seem peculiar to many people. However, it can be explained using the IPA phonetic transcription. The correct pronunciation of Sithe is /s-aɪ-ð/ where "s" sounds like "s" in sun, "aɪ" sounds like "i" in find, and "ð" sounds like "th" in this. The presence of the letter "e" in the spelling of Sithe indicates that the word is a variation of the traditional spelling for "scythe" which is a tool used for cutting grass and crops.
&c.-see sythe.
Etymological and pronouncing dictionary of the English language. By Stormonth, James, Phelp, P. H. Published 1874.