The name Siddim in the Bible
The Valley of Siddim is a place full of tar pits near the Salt Sea, or perhaps there where the Salt Sea now is, because Siddim is mentioned before the destruction of Sodom and Gomorrah (Genesis 19). The Valley of Siddim is where the War of Four Against Five Kings was waged (Genesis 14). King Bera of Sodom and king Birsha of Gomorrah of the overcome pentapolitan coalition, flee and die in the tar pits of Siddim (Genesis 14:10).
Etymology of the name Siddim
The origin of the name Siddim (a plural word) is somewhat dubious but the candidates can all be found in the following word group:
The two most likely candidates are not all that different. One possibility is the verb שדד (sadad), meaning to harrow. The other possibility is the unused root שדה (sdh), which yields the noun שדי (saday), meaning field, land, and שדה (sadeh) field.
BDB Theological Dictionary lists a third possibility, namely a derivation of the word שד (shed), meaning demon. The Valley Of Siddim would then mean the Valley Of Demons.
Note that our word שׁד is spelled with a shin (dot to the right), while שׂדים (Siddim) is spelled with a sin (dot to the left). These dots were put there long after the Torah was written, so in those days these letters were not visually distinguished. But the name of this region came to us through antiquity as Siddim and not as Shiddim. The name Siddim may in fact have more to do with the name Sodom than with this unusual word for (or unusual idea of) demon.
The name Siddim may mean Furrows, Divisions, Fields or Demons. For a meaning of the name Siddim, Jones' Dictionary of Old Testament Proper Names reads Plains. NOBSE Study Bible Name List does not translate.