... is Google.
If I am unsure of the spelling of a word or not entirely sure of the meaning I just type it into the Chrome URL box and I end up with a Google search with corrected spelling and links to the definition by default.
Probably not as easy on an iPad of course ... but $50 for any iPad app seems exorbitant. Unless I am missing something, if the point of the app is to be a dictionary, you really don't need an app (rig up a web service or something?). Ok this app has sound bytes for pronunciation, but Dictionary.com app is $4.99 (does the same as well as voice recognition of words) and this Oxford Deluxe is $50? I am probably missing something ...
Also any app that asks for my credentials to any other app or account would not get installed to begin with. Seriously, who would give a dictionary app access to their twitter account? Who says I even have a twitter account?