Create a glossary term in a glossary.

Anyone who can edit the glossary can create its terms: organization
administrators, and roles on a project linked to the glossary whose
editing the glossary's permissions leave on. Creating terms needs a plan
that supports glossary editing.

A 409 means another term of the glossary already has one of the new
term's variants with the same part of speech, or the glossary has no
resource to hold terms.