lubber's line vs lubber's mark

lubber's line and lubber's mark both are nouns.

Word	Noun	Adjective	Verb	Adverb
lubber's line	Yes	No	No	No
lubber's mark	Yes	No	No	No

As nouns, lubber's line and lubber's mark are synonyms defined as:

lubber's line and lubber's mark: a fixed line on a ship's compass indicating its heading

Other synonyms of lubber's line include lubber's point, lubber line.

lubber's line (noun)	lubber's mark (noun)
a fixed line on a ship's compass indicating its heading	a fixed line on a ship's compass indicating its heading