What does the etymology theme do? Allow you to add the etymologies of place names?

https://mapcomplete.org/etymology links objects (mostly streets, but also parks, schools, ...) to the Wikidata enitity of of what that street was _named_ after.

If the link is already there, it shows the relevant Wikipedia page. E.g. the 'Willow Street' would show the Wikipedia page on willows.

As a downstream effect: those links are also used in https://equalstreetnames.org/ to make gendered maps.