Other forms: directives; directively
A directive is an order or official notice that comes from an authority. The directive from your boss instructing all employees to wear silly hats on Fridays might be hard to take seriously.
Directives often come from employers, governments, supervisors, judges, or other authority figures. A math teacher might issue a directive to all students banning smart phones in the classroom after the school principal releases a directive instructing all math teachers to find ways to cut down on cheating during exams. Directive is also an adjective, meaning "helping to guide or manage."