While I know people understandably dislike Onyx Boox for their disregard for the GPL, their Android-based e-ink readers are exactly this. Their built in reader has offline dictionary support of its own, but as they are Android devices (albeit an older version and with a bit of hassle to get the Play Store on it besides their limited store), it can run standard Android apps -- I use it for both ebooks and for reading magazines from my library with Libby.