Money; originally, money obtained dishonestly. For example, She didn't like the job but loved the filthy lucre in the form of her weekly paycheck. This term comes from the Bible (Titus 1:11), where it refers to those who teach wrongly for the sake of money. In time it came to be used loosely, and usually jokingly, for money in general, and in the mid-1900s gave rise to the jocular slang term the filthy for “money.” Although both versions may be dying out, the expression filthy rich, for “extremely wealthy,” survives.
See 40 examples of "filthy lucre" at SKELL, here.