ran'-bo (qesheth, translated "a bow"; iris, "rainbow"):
As most of the rainfall in Palestine is in the form of short heavy showers it is often accompanied by the rainbow. Most beautiful double bows are often seen, and occasionally the moon is bright enough to produce the bow. It is rather remarkable that there are so few references to the rainbow in the Bible. The Hebrew qesheth is the ordinary word for a bow, there being no special word for rainbow.
The interpretation of the significance of the bow in the sky is given at the close of the story of the flood, where it is called "the token of the covenant" of Yahweh with Noah that there should be no more flood:
"I do set my bow in the cloud, .... and the waters shall no more become a flood to destroy all flesh" (Genesis 9:13,15). This addition to the story of the flood is not found in other mythical accounts. The foundation for the interpretation of the bow in this way seems to be that while His bow is hung in the sky God must be at peace with His people. The glory of God is likened to "the appearance of the bow that is in the cloud in the day of rain" (Ezekiel 1:28). The rainbow forms a striking part of the vision in Revelation 4:3: "And there was a rainbow round about the throne."
Alfred H. Joy