Rashi on Genesis 21:20/רש"י על בראשית כ״א:כ׳

1רבה קשת AN ARCHER — One who shoots arrows by a bow.

2(This is the explanation of רבה קַשָּׁת he is so designated after his occupation, that of a bow-man — just as חַמָּר denotes one who is an ass driver, גַּמָּל a camel driver, צַיָּד a huntsman; consequently the ש has a Dagesh (which distinguishes all these forms). — He used to live in the wilderness and rob travelers. It is to this the statement refers, (15:12) ידו בכל “his hand shall be against everyone, etc.”