balloon

accelerate, accumulate, appreciate, boom, build up, burgeon (also bourgeon), climb, enlarge, escalate, expand, gain, increase, mount, multiply, mushroom, proliferate, rise, roll up, snowball, spread, swell, wax

bag, beetle, belly, billow, bulge, bunch, jut, overhang, poke, pooch [chiefly dialect], pouch, pout, project, protrude, stand out, start, stick out, swell