Mawj is a wave; the phrase ka-mawji al-baḥr evokes a boundless, formidable night. Sudūl refers to hanging curtains or drapes that obscure what lies behind them. Arkhā means to let something down or slacken it.
Humūm is the plural of hamm, denoting worry, grief, and mental pressure. Anwāʿ emphasizes plurality of kinds: the poet does not specify a single sorrow but the accumulation of anxieties.
Two images work differently: the waves suggest vastness and agitation, whereas the curtains suggest enclosure and obscuration. Reducing both to the single word “darkness” would obscure the poem's carefully layered sensory design.