Other forms: boomingly
Something that's booming is growing fast or becoming prosperous, like your booming lemonade stand, which has the neighbors lining up down the block to buy a cup.
Use this adjective to describe an incredibly successful business, like the booming fireworks sales before the Fourth of July, or anything else that's making money, like your city's booming economy. A different meaning is "deep and resonant," as in a basso opera singer's booming voice. This definition is the older of the two, from boom, "make a deep sound," with the "thriving" meaning from a later use of boom, "burst into prosperity."