For 5 days only, the Japanese English High Frequency Words Dictionary (for Kindle Paperwhite) is available for free! Please go to Amazon and one-click purchase it. It might work with other Kindles besides the Paperwhite. If it does, please leave a review on Amazon and let everybody know. On Kindle Fire (tablet computers), you cannot set the default dictionary for look ups. Also be aware that the Kindle itself actually does the look up, not the dictionary. The Kindle dis-inflects verbs to the dictionary form before looking it up, so you might not always get the exact word you selected in your book as the result even if that word is in the dictionary. There is nothing that dictionary publishers can do about this.
Here are links to the dictionary in the various country stores of Amazon: