distress signal vs SOS

distress signal and SOS both are nouns.

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

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

distress signal: 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 signal include Mayday.

distress signal (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