green flag

noun

(in automobile racing) a green-colored flag that is used to signal the start of a race.

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British Dictionary definitions for green flag

Green Flag

noun

an award given to a bathing beach that meets EU standards of cleanliness

Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012