It seems that Handmark sells a few Oxford dictionaries on the Market. The OED and the American w/thesarus are there, but the Consice OED doesn't seem to be available any more. Like I said before, it appears that you have to use these standalone, which isn't very convenient when reading an ebook.
https://market.android.com/search?q=oxford&so=1&c=apps
From what I can tell, it looks like Handmark just put an Android app wrapper around the old Palmpilot database dictionary files. That being the case, I don't see why a lookup couldn't be done from within an Android ereader. I used to have that capability many years ago on a Windows PDA.
I'm not stuck on the OED necessarily. I do want whatever dictionary is used to be very comprehensive, including archaic and uncommon words.
Joe