J. Joosten in (שערי לשון מחקרים בלשון העברית, p. *51 is probably correct in identifying this word with a shin as a hapax in Syriac Ben Sira, but given that the etymon is surely with original śin, otherwise reflected as semkath in Syriac, it must be due to an error by the Syriac "translator" from the original JLA text.