The term 'increase rapidly' can be described by several crossword solutions, such as 'BALLOON' (7 letters), 'PROLIFERATE' (11 letters), 'SNOWBALL' (8 letters), 'runup' (5 letters), and 'shootup' (7 letters). These words all describe a rapid increase in size or quantity, with 'BALLOON' suggesting a gradual but steady increase, 'PROLIFERATE' suggesting a rapid spread, 'SNOWBALL' suggesting an exponential increase, 'runup' suggesting a sudden increase, and 'shootup' suggesting a sharp and sudden increase.