[DuckieTigger]

Originally Posted by ZodWallop

In English at least, Kindle is known for having a much better dictionary than Nook or Kobo (I forget which one it uses though). Not sure if their Spanish dictionary is as good.

There is multiple choices for free dictionaries:

For English there is:
Oxford Dictionary of English (2006 edition)
The New Oxford American Dictionary ( 2nd ed 2008 ebook edition)

For Spanish there is:
Real Academia Española el Diccionario de la lengua española (300 year edition / 23rd edition)

From reviews the spanish dictionary is supposed to be good as it also includes usage of words outside of Spain (e.g. for South America).