This is something we previously used in some of our documentation and support in Remarkup could be useful. Current solution is to convert the <dl> usage to <table>'s but since definition lists are a very simple and similar syntax I figured I'd file a feature request.
See here for more info on definition list syntax: https://developer.mozilla.org/en-US/docs/Web/HTML/Element/dl
What do you want to type into a text field to produce a definition list? (I can't immediately find any syntax in Markdown.)
It looks like Mediawiki uses this syntax:
;item-1 :definition-1 ;item-2 :definition-2-1 :definition-2-2
I suppose we could do the same. That syntax isn't super friendly for avoiding false positives in discussion of source code, but probably not terrible.
This request seems very niche, so I don't currently plan to pursue this. It may be possible to implement it as an extension.