Document the glossary as an alphabetically sorted table of the most important terms that are used in architecture and development. Include recurring business or requirements terminology, if these are not defined elsewhere.
You may include normative translations to other languages, if stakeholders work in various languages.
The glossary might be identical or similar to the „ubiquitous language“ from Domain-Driven-Design (and therefore can also be contained in arc42 section 8 (crosscutting concepts))