@sev At first they meant somewhat different things but today they are almost interchangeable since EDA kinda died out as its own thing and modern day ECAD just looks like EDA.

Originally ECAD was, similar to traditional CAD, int he sense that you designed things in 3D with a consideration of the dimensions and ultimately its compatibility with the case as you moved along. EDA however would largely have the developer focus mainly at the schematic level and the traces on the board without much regard tot he 3D layout. Though with the addition of 3D models in EDA and with ECAD integration in better with schematics the two have met in the middle and really arent different things anymore.

Thats how it was explained to me anyway.