Things that bombinate hum or buzz. A novice beekeeper might complain, "When the bees all bombinate like that, it makes me nervous!"
The sound of chatter in a coffee shop might bombinate around you as you try to concentrate on your book, and your dad might bombinate as he tidies the kitchen, humming and murmuring to himself. You bombinate when you produce a buzz of noise or activity. The word has a Latin root, bombinare, a variation on bombitare, "to hum or buzz," which comes from bombus, "a deep, hollow sound."