national flag vs allegory

national flag and allegory both are nouns.

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

As nouns, allegory is a hypernym of national flag; that is, allegory is a word with a broader meaning than national flag:

Other hypernyms of national flag include flag, emblem.

national flag (noun)	allegory (noun)
an emblem flown as a symbol of nationality	a short moral story (often with animal characters)
	an expressive style that uses fictional characters and events to describe some subject by suggestive resemblances; an extended metaphor
	a visible symbol representing an abstract idea