One of the mysteries of the English language finally explained.
1The heartwood of the oak.
2Figurative. A person with a strong, courageous nature, especially a brave and loyal soldier or sailor; (also) a courageous or valorous spirit. Frequently in plural Compare "heart". Now somewhat archaic.
3In plural form Hearts of Oak. (The members of) an Irish non-sectarian organization which protested, often violently, against taxes for the building of new roads, and tithes exacted by the Church of Ireland. Compare Oakboy. historical in later use.
Late Middle English. From heart + of + oak. With use in sense 2 compare heart.
heart of oak/hɑːt əv ˈəʊk/
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