Related Clues:

• Participate
• Add to the club
• Join the club
• Sign up for a class
• Sign up, as for a class
• Join the student body
• Sign up, variantly
• Register for a class (Var.)
• Join the class
• Register for (with "in")
• Register, as for a course (Var.)
• Loner inclined to join in
• Join up, sing on
• Sign on, register
• Join up, sign on