The Collaborative International Dictionary
To be on the anvil
Anvil \An"vil\, n. [OE. anvelt, anfelt, anefelt, AS. anfilt, onfilt; of uncertain origin; cf. OHG. anafalz, D. aanbeld.]
An iron block, usually with a steel face, upon which metals are hammered and shaped.
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Anything resembling an anvil in shape or use. Specifically (Anat.), the incus. See Incus.
To be on the anvil, to be in a state of discussion, formation, or preparation, as when a scheme or measure is forming, but not matured.
--Swift.