There are multiple origins and meanings for the name:
1. Greek name (δεινός) [dinos] - "formidable, awesome, troublous"
2. Gaelic dinas meaning - "city" + Emrys="fortified city of Ambrosius"
Dinas Emrys Arthur legend name of a fortified city given to Merlin Ambrosius by Vortigern after his celebrated prophecy concerning the fate of Britain.