weather deck vs topside

weather deck and topside both are nouns.

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

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

weather 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 weather deck include poop deck.

weather 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