Ugaritic

ṯ̣lmt - darkness (DUL 1004)

Cf. also probably γlmt with the same meaning (ibid. 320).

PS
*ṯ̣lm - to be dark, black (Bulakh 2003: 57; Bulakh 2006: 738; 740; Kogan 2011: 198; Kogan 2015: 237)