topside vs shelter deck

topside and shelter deck both are nouns.

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

As nouns, shelter deck is a hypernym of topside; that is, shelter deck is a word with a broader meaning than topside:

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

Other hypernyms of topside include weather deck.

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