rocker

Concise Oxford English Dictionary © 2008 Oxford University Press:
rocker/ˈrɒkə(r)/

▶noun

• 1 a person who performs, dances to, or enjoys rock music.

  ■ a rock song.

  ■ Brit. a young person, especially in the 1960s, belonging to a subculture characterized by leather clothing, riding motorcycles, and a liking for rock music.

• 2 a rocking chair.

• 3 a curved bar or similar support on which something such as a chair can rock.

  ■ a rocking device forming part of a mechanism.

• 4 the amount of curvature in the longitudinal contour of a boat or surfboard.

– phrases
off one's rocker informal mad.