distress call vs SOS

distress call and SOS both are nouns.

Word	Noun	Adjective	Verb	Adverb
distress call	Yes	No	No	No
SOS	Yes	No	No	No

As nouns, SOS is a hyponym of distress call; that is, SOS is a word with a more specific, narrower meaning than distress call:

distress call: an internationally recognized signal sent out by a ship or plane indicating that help is needed
SOS: an internationally recognized distress signal in radio code

Other hyponyms of distress call include Mayday.

distress call (noun)	SOS (noun)
an internationally recognized signal sent out by a ship or plane indicating that help is needed	an internationally recognized distress signal in radio code