The untranslatable refers to a language-based formation that escapes meaning. Structurally susceptible to being identified, the untranslatable raises the question of how it should be conveyed. In the field of psychoanalysis, this linguistic concept invites us to review certain fundamental aspects of practice and theory. From this point of view, the recurrence of translingualism in Freudian clinical cases indicates the untranslatable as an element of the formation of the symptom. A logical articulation also arises with the paternal function of transmission of the name and the prohibition of incest. The Lacanian notions of the letter, of the littoral and of non-specularity additionally provide a few interesting versions of the untranslatable. Exploration of these different theoretical aspects will enable us to demonstrate that sex and modalities of gender give the logical function of the untranslatable a subjective form. A few clinical and political reflections will be drawn from this latter observation.