oscillate

Concise Oxford English Dictionary © 2008 Oxford University Press:
oscillate /ˈɒsɪleɪt/

▶verb

• 1 move or swing back and forth in a regular rhythm.

  ■ fluctuate between two states, limits, opinions, etc.

• 2 Physics move or vary with periodic regularity.

  ■ cause an electric current or voltage to behave thus.

– derivatives
oscillation noun,
oscillator noun,
oscillatory /ɒˈsɪlət(ə)ri, ˈɒsɪləˌt(ə)ri/ adjective.

– origin C18 (earlier (C17) as oscillation): from L. oscillat-, oscillare ‘to swing’.