[1] Likewise or similarly in other lexica; references at Photius sigma139 Theodoridis. The gloss is genitive plural, so presumably the headword -- quoted from somewhere -- is too (from an unattested nominative selmo/s; the normal word is neuter se/lma). For the glossing word see sigma 92.
[2] Mount Selmon or Zalmon (Judges 9:48, etc.).
[3] This addition, also in Hesychius, relates to Psalm 67.15 LXX ("the kings shall be made snow-white in Selmon").