allegory vs red flag

allegory and red flag both are nouns.

Word	Noun	Adjective	Verb	Adverb
allegory	Yes	No	No	No
red flag	Yes	No	No	No

As nouns, red flag is a hyponym of allegory; that is, red flag is a word with a more specific, narrower meaning than allegory:

allegory (noun)	red flag (noun)
a short moral story (often with animal characters)	something that irritates or demands immediate action
an expressive style that uses fictional characters and events to describe some subject by suggestive resemblances; an extended metaphor	a flag that serves as a warning signal
a visible symbol representing an abstract idea	the emblem of socialist revolution