orlop deck vs fourth deck

orlop deck and fourth deck both are nouns.

Word	Noun	Adjective	Verb	Adverb
orlop deck	Yes	No	No	No
fourth deck	Yes	No	No	No

As nouns, orlop deck and fourth deck are synonyms defined as:

Other synonyms of orlop deck include orlop.

orlop deck (noun)	fourth deck (noun)
the fourth or lowest deck	the fourth or lowest deck