sliding keel vs centreboard

sliding keel and centreboard both are nouns.

Word	Noun	Adjective	Verb	Adverb
sliding keel	Yes	No	No	No
centreboard	Yes	No	No	No

As nouns, sliding keel and centreboard are synonyms defined as:

sliding keel and centreboard: a retractable fin keel used on sailboats to prevent drifting to leeward

Other synonyms of sliding keel include centerboard, drop keel.

sliding keel (noun)	centreboard (noun)
a retractable fin keel used on sailboats to prevent drifting to leeward	a retractable fin keel used on sailboats to prevent drifting to leeward