firing line vs social class

firing line and social class both are nouns.

Word	Noun	Adjective	Verb	Adverb
firing line	Yes	No	No	No
social class	Yes	No	No	No

As nouns, social class is a hypernym of firing line; that is, social class is a word with a broader meaning than firing line:

firing line: the most advanced and responsible group in an activity
social class: people having the same social, economic, or educational status

Other hypernyms of firing line include class, socio-economic class, stratum.

firing line (noun)	social class (noun)
the most advanced and responsible group in an activity	people having the same social, economic, or educational status
the line from which soldiers deliver fire