shelter deck vs topside

shelter deck and topside both are nouns.

Word	Noun	Adjective	Verb	Adverb
shelter deck	Yes	No	No	No
topside	Yes	No	No	No

As nouns, topside is a hyponym of shelter deck; that is, topside is a word with a more specific, narrower meaning than shelter deck:

shelter deck: upper deck having no overhead protection from the weather, but sheltering the deck below
topside: (usually plural) weather deck; the part of a ship's hull that is above the waterline

Other hyponyms of shelter deck include poop deck.

shelter deck (noun)	topside (noun)
upper deck having no overhead protection from the weather, but sheltering the deck below	(usually plural) weather deck; the part of a ship's hull that is above the waterline