Definition of Arcturus in US English:

Arcturus

proper noun

Astronomy
  • The fourth brightest star in the sky, and the brightest in the constellation Boötes. It is an orange giant.

Origin

From Greek arktos ‘bear’ + ouros ‘guardian’ (because of its position in line with the tail of Ursa Major).

Pronunciation

Arcturus

/ˌärkˈtyo͝orəs/