Someone who is ebullient is bubbling over with enthusiasm, so it shouldn't be much of a surprise that ebullient derives from the Latin verb ebullire, which means "to bubble out." When ebullient was first used in the late 1500s its meaning hewed closely to its Latin source: ebullient meant "boiling" or "bubbling," and described things like boiling water and boiling oil. Only later did the word's meaning broaden to encompass emotional agitation as well as the roiling of a boiling liquid.