Vernacular languages have served as media of science education in colonial and postcolonial South Asia, but how was modern scientific knowledge translated into these languages and made available for non-English reading publics? This article draws attention to the overlooked genre of the glossary of technical terminology, conceived as the source list of the very words needed for vernacular scientific discourse. Focusing on the Nagari Pracharini Sabha’s Hindi Scientific Glossary (HSG, 1906), I analyse the linguistic, epistemic and political strategies by which technical terms and chemical nomenclature were rendered meaningful and authoritative for the Hindi science learner. The making of the HSG exemplifies the tensions of crafting authoritative equivalences faced by Indian language activists in a colonial episteme. Situating the glossary in its colonial genealogy and within a multilingual imaginary of science translation and language activism, this article demonstrates the inter-vernacular resonance and quest for lexicographic authority in Indian projects of terminology.