The U. of Toronto was among the very first Libraries to go digital -- in short, they were years ahead of their times. There are many online digital archives of Monier William's Skt.-Eng. Dictionary. This one is AFAIK the best in quality. Use it as a final reference if other digital copies, whether html or unicode, have errors or inconsistencies. Prefer the color version to the B&W one, as it is more faithful to the original, and not that much "heavier" as far as downloads go. You will need a system with enough RAM to handle the file, about 129 MBytes in size.
MW's dictionary is still your best bet when learning Sanskrit, at least in my experience.

HELLO