Definition of rose-a-ruby in US English:

rose-a-ruby

(also rose-a-rubie)

noun

historical
  • The plant pheasant's eye, Adonis annua, which has crimson flowers.

Origin

Late 16th century; earliest use found in John Gerard (c1545–1612), herbalist. Apparently from rose + a + ruby.

Pronunciation

rose-a-ruby

/ˈrəʊzəˌruːbi/