From an unused root meaning to hide; winter (as the dark season) -- winter.
Englishman's Concordance
1) winter, rainy season Part of Speech: noun masculine A Related Word by BDB/Strong’s Number: from an unused root meaning to hide Same Word by TWOT Number: 1549.1
Brown-Driver-Briggs
סתו Kt, סְתָיו Qr noun masculinewinter (loan-word from Aramaic; compare Syriac , ᵑ7סִיתְוָא; Arabic Lane1504; probably originally ׳שׂ, compare SchwIdioticon 64; on ו as old nominative ending (׳ס for šutayu) compare LagBN 190 Anm.); — הַסְּתָ֯ו עָבָ֑רSongs 2:11.
Songs 2:11 HEB:[הַסְּתָו כ] (הַסְּתָ֖יו ק) עָבָ֑ר NAS: For behold, the winter is past, KJV:For, lo, the winter is past, the rain INT: For behold winter is past the rain