Usually the url schemes are something like this: dictionary app://{text}, in marvin 3 you should put "text" in the place holder, in marvin 2 it's "define" instead. Some dictionaries have different kinds of url schemes for example here is the url scheme for Terminology app:
https://agiletortoise.zendesk.com/hc...gy-URL-schemes
And sometimes somebody found out a url scheme and a google search could help, and also you can extract url schemes from the 'Info.plist' file in your app's .ipa file. here's how:
https://www.reddit.com/r/workflow/co...me_of_any_app/