From Latin (14th century), from Greek 'glôssa (γλῶσσα)' ("tongue; language; obscure word").
An alphabetical list of words relating to a specific subject, text, or dialect, with explanations; a brief dictionary.
From Latin 'glossārium' (a collection of glosses), from 'glossa' (an unusual or foreign word requiring explanation), borrowed from Greek 'glôssa' (γλῶσσα, tongue, language, obscure word). Originally 'glôssa' meant the physical tongue, then extended to mean language itself, and then specifically a word needing explanation — because foreign or archaic words felt as strange as a foreign tongue. Medieval scholars wrote explanatory 'glosses' in manuscript margins, and
'Glossolalia' — speaking in tongues — comes from the same Greek root: 'glôssa' (tongue) plus 'laliá' (speech). Medieval monks preserving glossaries of rare Latin words and Pentecostal worshippers speaking in tongues are etymologically engaged in the same activity: dealing with strange languages.