How to Cite verbalworkout.com
To cite the website (rather than any particular page):
Book Vocabulary. verbalworkout.com, n.d. Web. dd Mmm. yyyy.
dd = day of month in two digits; e.g., the first of the month is "01"
Mmm = month as Jan, Feb, Mar, Apr, May, Jun, Jul, Aug, Sep, Oct, Nov, or Dec
yyyy = year such as "2014"
To cite a particular page or set of pages (which MLA would refer to as an article) the article title and specific URL needs to be added. Here is an example using the standard book post-reading assignment for To Kill a Mockingbird:
"Vocabulary Review for To Kill a Mockingbird." verbalworkout.com. verbalworkout.com, n.d. Web. dd Mmm. yyyy. <https://www.verbalworkout.com/t/t1013sbr.htm>
Where dd, Mmm, and yyyy are as described above.