From an unused root meaning to set as the sun; dusky -- very dark.
Englishman's Concordance
1) gloomy, dark Part of Speech: adjective A Related Word by BDB/Strong’s Number: from an unused root meaning to set as the sun Same Word by TWOT Number: 145b
Brown-Driver-Briggs
אָפֵלadj. gloomy, of day of ׳יAmos 5:20 ("" כשׁך opp נֹגַהּ) compareאֲפֵלָה .
Amos 5:20 HEB:וְלֹא־ א֑וֹר וְאָפֵ֖ל וְלֹא־ נֹ֥גַֽהּ NAS: of light, Even gloom with no KJV: and not light? even very dark, and no brightness INT: no of light gloom no brightness
