Vocabulary.com has a streamlined interface without advertisements. It offers narrative, in addition to academic, descriptions for the most frequently looked up words.
Empirical: If knowledge is empirical, it's based on observation rather than theory. To do an empirical study of donut shops, you'll need to visit every one you can find.
Empirical: derived from experiment and observation rather than theory.
There are 100 million sentence examples of the word in use from news, medicine/science, technology and other disciplines. Audio files of defined terms are available in computerized MP3 format.
While helpful, this site also uses a lot of vernacular (jargon) which may not be known to non-native speakers, in its definitions. Additionally, the sentence examples are not cited, making it difficult to go back to the source to read further.