Asteroid 21561, Masterman, was discovered on August 28, 1998 by the Lincoln Laboratory Near-Earth Asteroid Research Team at Socorro, New Mexico. It has a period of 4 years, 144 days.
It was named for Oklahoma City high school student Mary Masterman (born 1989) who was got first place in the 2006 Intel International Science and Engineering Fair for her physics project.
Mary Masterman
The meaning of asteroid Masterman seems to be: domineering or dominating authority.