noun
A multicoloured arch in the sky, produced by prismatic refraction of light within droplets of rain in the air.
Any prismatic refraction of light showing a spectrum of colours.
(often used with “of”) A wide assortment; a varied multitude.
(figurative) An illusion; a mirage.
(baseball) A curveball, particularly a slow one.
(soccer) A trick in which the player makes the ball arc over the opponent's head using both feet; rainbow kick
(poker slang) In Texas hold 'em or Omaha hold 'em, a flop that contains three different suits.
Rainbow trout.
(figuratively, sometimes derogatory) A person within the LGBT community.
adjective
Multicolored, especially if in rainbow order.
(attributive, chiefly US) Made up of several races or ethnicities, or (more broadly) of several cultural or ideological factions.
(attributive) LGBT.
(poker, chiefly of a flop) Composed entirely of different suits.
(mathematics, cryptography) Of or pertaining to rainbow tables.
verb
(transitive) To brighten with, or as with, a rainbow; to pattern with the colours of the rainbow.
(intransitive) To take the appearance of a rainbow.
(climbing) In climbing gyms where the rocks to climb are colored to indicate suggested climbing routes, to climb rocks of different colors, thereby ignoring such routes.