speech balloon vs speech bubble

speech balloon and speech bubble both are nouns.

Word	Noun	Adjective	Verb	Adverb
speech balloon	Yes	No	No	No
speech bubble	Yes	No	No	No

As nouns, speech balloon and speech bubble are synonyms defined as:

speech balloon and speech bubble: in cartooning, a rounded outline containing words.

speech balloon (noun)	speech bubble (noun)
in cartooning, a rounded outline containing words.	in cartooning, a rounded outline containing words.