Definition of black drop in English:

black drop

noun

  • 1Medicine. In singular or (rare) plural A dark-coloured liquid medicine composed of opium in vinegar or verjuice with various spices. Now historical.

  • 2Astronomy. A dark elongation of a planet's disc observed at the start and finish of solar transits of Venus and Mercury when the disc of the planet is just inside and touching the edge of the sun's disc, so that the planet briefly has a pear-shaped appearance elongated towards the sun's edge.

Origin

Early 19th century; earliest use found in The Caledonian Mercury. From black + drop.

Pronunciation

black drop

/ˌblak ˈdrɒp/