portentous vs prodigious

portentous and prodigious both are adjectives.

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

As adjectives, portentous and prodigious are synonyms defined as:

portentous (adjective)	prodigious (adjective)
puffed up with vanity	far beyond what is usual in magnitude or degree
ominously prophetic	so great in size or force or extent as to elicit awe
of momentous or ominous significance	of momentous or ominous significance