Definition of iron blue in US English:

iron blue

noun

  • 1A greyish-blue colour.

  • 2Angling. A small dark mayfly of the genus Baetis; an artificial fly made in imitation of it.

  • 3Any of various blue pigments containing iron, especially. Prussian blue.

adjective

  • Of a greyish-blue colour; designating this colour.

Origin

Late 17th century; earliest use found in John Dryden (1631–1700), poet, playwright, and critic. From iron + blue.

Pronunciation

iron blue

/ˌʌɪən ˈbluː/