adamancy

ad·a·mant  (d-mnt, -mnt)

adj.

Impervious to pleas, appeals, or reason; stubbornly unyielding. See Synonyms at inflexible.

n.

1. A stone once believed to be impenetrable in its hardness.

2. An extremely hard substance.

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[From Middle English, a hard precious stone, from Old French adamaunt, from Latin adams, adamant-, from Greek, unconquerable, hard steel, diamond; see dem- in Indo-European roots.]

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ada·man·cy n.

ada·mant·ly adv.