Abarim Publications' online Biblical Hebrew Dictionary
The root-verb זבב (zbb) isn't used in the Bible, but in cognate languages it means to go hither and thither, move to and fro. This verb's sole derivative is the slightly more common masculine noun זבוב (zebub), meaning fly.
The fly, scholars suppose, was known as a creature that zips to and fro or bumbles hither and thither. In the Bible this noun occurs only in Ecclesiastes 10:1 (the death-bringing flies) and Isaiah 7:18 (as metaphor for the Egyptian army). And this noun is also immortalized in the name Beelzebub.
There may be a relation between our verb זבב (zbb) and the verb אזב ('zb).