Argument from false premises
A false premise can also be a premise that is poorly defined, which makes the conclusion questionable.  The following joke from Plato and a Platypus Walk Into a Bar illustrates the point: "An old cowboy goes into a bar and orders a drink.  As he sits there sipping his whiskey, a young lady sits down next to him.  ... She says, 'I'm a lesbian.  I spend my whole day thinking about women. ...' A little while later, a couple sits down next to the old cowboy and asks him, 'Are you a real cowboy?' He replies, 'I always thought I was, but I just found out I'm a lesbian'."  The mistake the cowboy makes is that he assumes that the definition of a lesbian is somebody who spends the "whole day thinking about women", without including the fact that a lesbian is a homosexual female.  The cowboy is neither homosexual nor female; therefore, he is not a lesbian.