portentous vs overblown

portentous and overblown both are adjectives.

Word	Noun	Adjective	Verb	Adverb
portentous	No	Yes	No	No
overblown	No	Yes	No	No

As adjectives, portentous and overblown are synonyms defined as:

Other synonyms of portentous include grandiloquent, pompous, pontifical.

portentous (adjective)	overblown (adjective)
puffed up with vanity	past the stage of full bloom
ominously prophetic	puffed up with vanity
of momentous or ominous significance