Hardwood

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Old English wudu, from a Germanic word related to Welsh gwŷdd ‘trees’.

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hard +‎  wood

etymonline

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hardwood (n.)

1560s, from hard (adj.) + wood (n.). That from deciduous trees, as distinguished from that from pines and firs. Bartlett ("Dictionary of Americanisms," 1848) defines it as "A term applied to woods of solid texture that soon decay, including generally, beech, birch, maple, ash, &c. Used by shipwrights and farmers in Maine, in opposition to oak and pine."