The paper presents the problem of etymologisation (folk etymology), which involves the false genealogy of meanings of concepts. Exploration and “discovering“ of such false or projected meanings, as a result of the use of false genealogy has already been examined by specialists of language studies. However, it is important to note that etymologisation affects also philosophy. The paper attempts to characterize main features of this form of folk etymology and proposes to develop Hans Schnädelbach’s category of the philosophical “hermeneutic disease” (morbus hermeneuticus) to “etymological disease” (morbus etymologicus). This attempt helps to formulate the answer to the question why philosophers are tempted by etymologisations and why they so often succumb to this temptation. The main causes of this process revealed by philosophers are: the pursuit of surprise, which is the starting point for philosophical reflexion; the strong devotion to tradition and long history of their discipline; the permanent striving for both freshness and depth of philosophical language, and some kind of faith in the myth of the fundamental (antique or even older) source of all knowledge. Although the philosophical form of the folk etymology is recognized in the paper as a substantial threat, at the same time there is some hope that studies on etymologisation may become an inspiration for philosophers.