This chapter addresses the dynamic and fluctuating terminology of sustainability and its complex background. Many branches of social science cover the concept of sustainability and their perspectives vary significantly (Sect. 3.1). Particular attention is given to linguistics, especially morphology and semantics, because sustainability is both expressed and explained by language units dealing with reality and fairness (Sect. 3.2). The term sustainability is not only a linguistic challenge, entailing the study of several languages, but in addition it is an ephemeral phenomenon from the spheres of ontology from metaphysics (what is real?) and ethics from axiology (what is morally right?) (Sect. 3.3). Such a linguistic and philosophical exploration, along with other findings, points out that sustainability has multi-disciplinary features and the meta dimension, i.e. it is the meta-sustainability (Sect. 3.4).