An unctuous hypocrite, a person who affects benevolence or pretends to have high moral principles; (also) a person who interferes officiously in the business of others. Frequently attributive. Also (occasionally) as adjective.
Mid 19th century; earliest use found in The Civil Engineer and Architect's Journal. From the name of Mr Pecksniff, a hypocritical character in Charles Dickens's novel The Life and Adventures of Martin Chuzzlewit.
To speak or act like a Pecksniff.
Early 20th century; earliest use found in George Bernard Shaw (1856–1950), playwright and polemicist. From Pecksniff.