Definition of blue cap in English:

blue cap

noun

  • 1Military
    historical, slang Military slang (now historical). Originally: a soldier belonging to the Royal Madras Fusiliers; (later) a soldier belonging to the Royal Dublin Fusiliers.

  • 2English Regional rare Chiefly English regional. The cornflower, Centaurea cyanus. Now rare.

  • 3Mining
    rare A bluish layer in a flame; specifically (Mining) a circle of bluish flame appearing above and around the wick of a safety lamp, indicating the presence of explosive gases. Compare "cap". Now rare.

Origin

Late 16th century (in an earlier sense). From blue + cap.

Pronunciation

blue cap

/ˌbluː ˈkap/