出典:Wiktionary
phenomenon + -logy, from Ancient Greek φαινόμενον (phainómenon, “thing appearing to view”), hence "the study of what shows itself (to consciousness)".
According to Heidegger's Introduction to Phenomenological Research, "the expression “phenomenology” first appears in the eighteenth century in Christian Wolff’s School, in Lambert’s Neues Organon, in connection with analogous developments popular at the time, like dianoiology and alethiology, and means a theory of illusion, a doctrine for avoiding illusion." (p.3)
phenomenology (countable かつ uncountable, 複数形 phenomenologies)