When you press a word in the Kindle iPad application, then you search the built in dictionary, and it works very well indeed.
You also get the opportunity to "Note", "Highlight" and "Share". Why not a "Copy" option? I am Danish and I have an English to Danish dictionary on my iPad and it would be very convenient to be able to paste the word into this dictionary. The built in English to English dictionary is very often good enough, but sometimes it would be nice with a translation into Danish.
An example: the word
Sparrow
will give this answer in an English to English dictionary:
a small finch-like Old World bird related to the weaver birds, typically with brown and grey plumage... and so on.
In English to Danish it is simply
Spurv a very common bird
I am aware that copy paste might be problematic for copyright reasons, but really, it can't be a problem with a single word!