An Etymological Dictionary of Astronomy and Astrophysics

1. The act of registering; registration.
   

2. A place where a register is kept; an office of registration.
   

3. The state of being registered (Dictionary.com).
   

4. In → computers, a part of the → central processing unit used to store configuration information about the → software installed on a computer.

See also: → register + -y.