Definition of on-beat in US English:

on-beat

adjective

Music
  • Corresponding in time with the most accented beat in the bar.

noun

Music
  • The most accented beat in a bar; also in analogous uses with respect to poetry, etc.

Origin

1960s; earliest use found in John o' London's. From on- + beat.

Pronunciation

on-beat

/ˈɒnˌbiːt/