Flush has 24 different meanings across 4 categories:
a poker hand with all 5 cards in the same suit
"He was thrilled to be dealt a royal flush at the beginning of the game."
a sudden rapid flow (as of water)
"he heard the flush of a toilet"
"there was a little gush of blood"
"she attacked him with an outpouring of words"
A group of birds that have suddenly started up from undergrowth, trees etc.
"She won the game when her opponent played a flush, revealing five hearts in a row."
A sudden flowing; a rush which fills or overflows, as of water for cleansing purposes.
A hand consisting of all cards with the same suit.
In plain English: A flush is a poker hand where all five cards are from the same suit, like hearts or spades.
"He hoped to get a royal flush during the poker tournament."
Usage: As a noun, flush refers to the sudden rush of water used for cleaning or a startled flight of birds taking off together. Use this term specifically when describing that momentary surge rather than a continuous flow.
To cause to take flight from concealment.
"The gardener flushed the soil with water to wash away all the excess fertilizer."
To cleanse by flooding with generous quantities of a fluid.
In plain English: To flush means to wash something clean using a lot of liquid.
"She quickly flushed the debris from the sink."
of a surface exactly even with an adjoining one, forming the same plane
"a door flush with the wall"
"the bottom of the window is flush with the floor"
Smooth, even, aligned; not sticking out.
"The carpenter sanded the wood until its surface was perfectly flush."
In plain English: Flush means neat and level with everything around it.
"The new kitchen cabinets have a flush mount to the wall."
From Middle English flusshen, fluschen, of uncertain origin. Compare dialectal flusk ("to fly at, startle a bird out of the bush") and flusker ("to flutter, fly irregularly"). Perhaps related to Middle English flasshen, flasschen, flaschen, see flash; or a Middle English blend of flowen ("to flow") + guschen ("to gush"). Compare Saterland Frisian flutskje, German Low German flutschen, German flutschen.