Shadow (Noun) - Vine's Expository Dictionary of New Testament Words
Shadow (Noun)[ 1,,G4639, skia ]
(a) of a shadow," caused by the interception of light, Mark 4:32, Acts 5:15; metaphorically of the darkness and spiritual death of ignorance, Matthew 4:16; Luke 1:79;
(b) of "the image" or "outline" cast by an object, Colossians 2:17, of ceremonies under the Law; of the tabernacle and its appurtenances and offerings, Hebrews 8:5; of these as appointed under the Law, Hebrews 10:1.
[ 2,,G644, aposkiasma ]
"a shadow," is rendered "shadow that is cast" in James 1:17, RV; the AV makes no distinction between this and No. 1. The probable significance of this word is "overshadowing" or "shadowing-over" (which apo may indicate), and this with the genitive case of trope, "turning," yields the meaning "shadowing-over of mutability" implying an alternation of "shadow" and light; of this there are two alternative explanations, namely, "overshadowing"
(1) not caused by mutability in God, or
(2) caused by change in others, i.e., "no changes in this lower world can cast a shadow on the unchanging Fount of light" [Mayor, who further remarks, "The meaning of the passage will then be, 'God is alike incapable of change (parallage) and incapable of being changed by the action of others'"].