noun

A brightly colored rubber sac that is inflated with air and then sealed at the neck, used as a children’s toy or a decoration.

the room was festooned with balloons and streamers

intransitive verb

Swell out in a spherical shape; billow.

the trousers ballooned out below his waist

swell,swell out,puff out,puff up,bulge,bulge out,bag,belly,belly out,fill,fill out,billow,billow out