The American Heritage Student Dictionary;

A newly updated version of our beloved dictionary for students in grades 6–10 (ages 11–16)

The American Heritage Student Dictionary, for students in grades 6–10 (ages 11–16), has been updated and contains more than 65,000 words, covering the vocabulary that students in this age group need to know. The definitions are clear and easy to read, and they are bolstered by abundant example sentences, letting readers see how words are used in context. Among the new words added in this latest update are science terms such as the newly discovered nihonium and oganesson and terms from popular culture and social media such as facepalm, stevia, and vlog.
 
This edition also has a full-color art program, with 2,000 color photographs and illustrations in the margins, retains its array of 400 feature notes, and also includes a carefully-crafted program of 200 fun-to-read quotations from young adult authors.
 
This is by far the best dictionary for this age group that is available today. At home or in class, it is the most useful and engaging resource on words a student could have.