Burgeon

Used in a sentence:

• The balloon began to slowly burgeon as they filled it the warm hair they would need lift off up into the stars.

Source: Wiktionary

Commentary:

Not so weird of a word for those of you who read more historical fiction. I think I’ve heard the term “burgeoned into a tall young man” a few too many times to make this word that weird. Little interesting fact, prior to meaning grow or expand, it used to be a noun that referred to the bud or sprout of a plant. That meaning is considered obsolete however.