Rainbow

Rainbow - (Easton's Bible Dictionary)

Caused by the reflection and refraction of the rays of the sun shining on falling rain. It was appointed as a witness of the divine faithfulness (Gen. 9:12-17). It existed indeed before, but it was then constituted as a sign of the covenant. Others, however (as Delitzsch, Commentary on Pentateuch), think that it "appeared then for the first time in the vault and clouds of heaven." It is argued by those holding this opinion that the atmosphere was differently constituted before the Flood. It is referred to three other times in Scripture (Ezek. 1:27, 28; Rev. 4:1-3; 10:1).

Rainbow - (Webster's 1828 Dictionary)

RA'INBOW, n. A bow, or an arch of a circle, consisting of all the colors formed by the refraction and reflection of rays of light from drops of rain or vapor, appearing in the part of the hemisphere opposite to the sun. When the sun is at the horizon, the rainbow is a semicircle. The rainbow is called also iris.

The moon sometimes forms a bow or arch of light, more faint than that formed by the sun, and called lunar rainbow. Similar bows at sea are called marine rainbows or sea bows.