The Collaborative International Dictionary
Water flag
Water flag \Wa"ter flag`\ (Bot.) A European species of Iris ( Iris Pseudacorus) having bright yellow flowers.
Wiktionary
water flag
n. A European iris with bright yellow flowers, ''Iris pseudacorus''.
Usage examples of "water flag".
To the popular mind in early days, the fluttering segment of the perianth suggested the waving of a flag, hence the origin of the names 'Yellow Flag,' 'Water Flag' and 'Sword Flag,' and corruptions of the name such as 'Flaggon,' 'Flaggon's' and perhaps 'Fliggers,' the latter stated to be applied to it from the motion of its leaves by the slightest breeze.