centreboard vs drop keel

centreboard and drop keel both are nouns.

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

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

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

Other synonyms of centreboard include centerboard, sliding keel.

centreboard (noun)	drop keel (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