Nothing wrong with it, depending on: (1) which dictionary; (2) whether the student reads the complete definition as well as all the definitions and understands all the contexts for those (or is willing to investigate those distinctions further).
Most of my students typically read partial definitions (omitting the “ands,” the “ors,” and the “especially in the sense of”). Diction relates to nuance, setting, and connotation, not to some minimalist, single denotation, and most 21st century students are too lazy and uncurious when it comes to word meanings. I wish more students would do what my siblings and I did in our childhoods: include dictionary and encyclopedia reading. I know that some elementary-grade homeschooled students do read dictionaries – yes, today.