I use the free to access lexical database wordnet from Princeton University for word definitions:
Princeton University “About WordNet.” WordNet. Princeton University. 2010. http://wordnet.princeton.edu
The English – Japanese example sentences have mostly been sourced from tangorin.com (an online free to use Japanese – English Dictionary). Sentences from the tangorin website were originally from the Tatoeba project. Sentences that are not taken from there are either written by myself or my wonderful contributors.
Tatoeba.org is a multilingual resource developed by Trang Ho and her collaborators. They have built upon the example sentence database from the Tanaka corpus. The Tanaka corpus was originally a project by Professor Yasuhito Tanaka and his students at Hyogo University. It is released it under a CC-BY licence.
Please see the following page for a more detailed history of the example sentences from the Tanaka corpus and its subsequent development: