This word is acceptable for play in the US & UK dictionaries that are being used in the following games:

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n. See masterpiece.

n. A piece done to prove possession of skill sufficient to be ranked a master.

n. A piece of quality, indicative of having been made by a master; a masterpiece.

n. An act of primary importance.

n. A main drain or irrigation channel.

n. Principal performance; masterpiece; chef-d'œuvre.

"His masterwork is the set of four Rabbit Angstrom novels, a thousand pages in all, one novel every ten years from 1960 to 1990."

plasterwork   

chariot'    shemade    few    creature    shadow-world    Shandy    fiddle-faddle    silence    case?'    Pernod