When men have names in their mouths without any determinate ideas in their minds whereof they are the signs
 John Locke, An Essay Concerning Human Understanding (1689). copy citation

Context

“and, Thirdly, thereby to convey the knowledge of things: language is either abused or deficient, when it fails of any of these three. First, Words fail in the first of these ends, and lay not open one man's ideas to another's view: 1. When men have names in their mouths without any determinate ideas in their minds whereof they are the signs: or, 2. When they apply the common received names of any language to ideas, to which the common use of that language does not apply them: or 3. When they apply them very unsteadily, making them stand now for one, and by and by for another idea.” source