Thanks very much!
Left and Right arrow keys – move to the previous/next highlighted word
k – mark the word as known
x – "ignore"
s – play the automatically generated text-to-speech audio
On a unknown highlighted word:
Up and Down arrow keys – move up or down in the list of hints and dictionaries
Enter – select first recommended definition
I'd also suggest that when selecting a definition for a new word, the red unknown highlighted word should turn green to signify you've seen it before and it's now a "Learning" word.