From the base of skia; shadiness, i.e. Obscurity (literally or figuratively) -- darkness.
see GREEK skia
STRONGS NT 4655: σκότοςσκότος, σκότους, τό, from Pindar down (see the preceding word, and σκοτία, at the beginning), the Sept. chiefly for חֹשֶׁך, darkness;
a. properly: Matthew 27:45; Mark 15:33; Luke 23:44; Acts 2:20; 2 Corinthians 4:6; αὕτη ἐστιν ἡ ἐξουσία τοῦ σκότους, this is the power of (night's) darkness, i. e. it has the power of rendering men bold to commit crimes, Luke 22:53; τά κρυπτά τοῦ σκότους (see κρυπτός), 1 Corinthians 4:5; of darkened eyesight or blindness: σκότος ἐπιπίπτει ἐπί τινα i. e. on one deprived of sight, Acts 13:11; in figurative discourse, εἰ οὖν ..., τό σκότος πόσον; if the light that is in thee is darkness, darkened (i. e. if the soul has lost its perceptive power), how great is the darkness (how much more deplorable than bodily blindness), Matthew 6:23, cf. Luke 11:35. by metonymy, put for a dark place: Matthew 8:12; Matthew 22:13; Matthew 25:30 (see ἐξώτερος); ζόφος τοῦ σκότους (see ζόφος), 2 Peter 2:17; Jude 1:13.
b. metaphorically, of ignorance respecting divine things and human duties, and the accompanying ungodliness and immorality, together with their consequent misery (see σκοτία): John 3:19; Acts 26:18; 2 Corinthians 6:14; Ephesians 6:12; Colossians 1:13; 1 Peter 2:9; (abstract for the concrete) persons in whom darkness becomes visible and holds sway, Ephesians 5:8; τά ἔργα τοῦ σκότους, deeds done in darkness, harmonizing with it, Romans 13:12; Ephesians 5:11; σκότους εἶναι, to be given up to the power of darkness (cf. Winer's Grammar, § 30, 5 a.), 1 Thessalonians 5:5; ἐν σκότει εἶναι, 1 Thessalonians 5:4; οἱ ἐν σκότει, Luke 1:79; Romans 2:19; ὁ λαός ὁ καθήμενος ἐν ἐκοτει, Matthew 4:16 R G T; ἐν σκότει περιπατεῖν, 1 John 1:6.