I give in-class exams in Canvas to larger classes (~200 students).  In our last exam, we discovered as student using the Mac dictionary function within the Canvas exam.  This means that the student was clicking with 3 fingers on her trackpad while hovering over a word in one of the exam questions and the definition of that word would pop up.  

Obviously this would be considered using an outside source for information and is considered to be cheating.  Is there a way to disable this function on students' computers while taking a Canvas exam (other than them having to shut off the function in system preferences)?

Thank you for any help anyone can provide!