I just typed in 'quotidian' to both apps. (It came up this weekend.)
Definr is very fast. It looks up words faster than I type so that the list of words at the bottom updates with each new letter. With IWS, I had to pause mid-word for a half-second in order to get an updated list. By the time I got a choice of words with IWS, I had finished typing and already made a typo.
Also, the interface for Definr is much more friendly looking and simple. Definr gives you the complete definition on the main page, instead of links to other definitions. And Definr is an easy name.
Sorry, but I liked Definr much better.
I haven't played with it enough to evaluate it on functionality, but as-is, it's not pretty enough to get popular. It's sad that aesthetics matter so much for a purely functional tool, but that's just how things are.
It does more than definr (e.g. pattern search). But it was met with indifference (except on StumbleUpon). Can you tell me where I screwed up?
May be I shouldn't have mentioned that I wrote it as a toy app? (but it IS a toy app) Picture needed? Looks ugly/too simple? Name too long? All I am able to come up with are some conspiracy theories: 'Definr creator lists Kevin Rose as friend in his Digg profile'; 'Ruby-On-Rails was mentioned' etc. But the real issue must be something else.
I think the fault is invisible to me as I created the tool. Hopefully I can learn a marketing lesson or two from this... Please help.