To insert surreptitiously, wrongfully, or without warrant; to interpolate; to pass off (something spurious or counterfeit) as genuine, true, or worthy; -- usually followed by
in.
“Lest negligence or partiality might admit or foist in abuses and corruption.”
— R. Carew.
“When a scripture has been corrupted . . . by a supposititious
foisting of some words in.”
— South.