The term 'grew rapidly' can be described in three different ways: BOOMED (6 letters), MUSHROOMED (10 letters), and shot up (6 letters). Booming is a term used to describe a sudden, rapid increase in size or activity. Mushrooming is a term used to describe a rapid growth in size or number. Finally, shot up is a term used to describe a sudden, rapid increase in value or amount. All three terms accurately describe the phrase 'grew rapidly'.