The defender of the view that expressions have meanings which determine extensions seems forced to say that “line” and “door” are homophonous expressions, like “bank”. But that seems implausible; when one uses the expressions “fishing line” and “line of thought” one seems to be using “line” in recognizably the same sense. (This is a point of contrast with standard examples of homophony, as when uses “bank” once to refer to a financial institution and then later to refer to the side of a river.)