Flag

Two different things are called a flag here. One is a water plant of the river’s edge. Job asks, “can the flag grow without water?” (Job 8:11), and Isaiah 19:6 says the “reeds and flags shall wither” when the rivers are turned away. The baby Moses is laid in “an ark of bulrushes” in the same kind of place (Exodus 2:3). The other is a banner. Isaiah speaks of an ensign lifted on the mountains for the nations to see, and of the root of Jesse standing “for an ensign of the people” (Isaiah 11:10).

11 verses

Exodus

Exodus 2:3

And when she could not longer hide him, she took for him an ark of bulrushes, and daubed it with slime and with pitch, and put the child therein; and she laid it in the flags by the river's brink.

Exodus 2:5

And the daughter of Pharaoh came down to wash herself at the river; and her maidens walked along by the river's side; and when she saw the ark among the flags, she sent her maid to fetch it.

Job

Job 8:11

Can the rush grow up without mire? can the flag grow without water?

Psalms

Psalms 74:4

Thine enemies roar in the midst of thy congregations; they set up their ensigns for signs.

Isaiah

Isaiah 5:26

And he will lift up an ensign to the nations from far, and will hiss unto them from the end of the earth: and, behold, they shall come with speed swiftly:

Isaiah 11:10

And in that day there shall be a root of Jesse, which shall stand for an ensign of the people; to it shall the Gentiles seek: and his rest shall be glorious.

Isaiah 11:12

And he shall set up an ensign for the nations, and shall assemble the outcasts of Israel, and gather together the dispersed of Judah from the four corners of the earth.

Isaiah 18:3

All ye inhabitants of the world, and dwellers on the earth, see ye, when he lifteth up an ensign on the mountains; and when he bloweth a trumpet, hear ye.

Isaiah 19:6

And they shall turn the rivers far away; and the brooks of defence shall be emptied and dried up: the reeds and flags shall wither.

Isaiah 30:17

One thousand shall flee at the rebuke of one; at the rebuke of five shall ye flee: till ye be left as a beacon upon the top of a mountain, and as an ensign on an hill.

Isaiah 31:9

And he shall pass over to his strong hold for fear, and his princes shall be afraid of the ensign, saith the LORD, whose fire is in Zion, and his furnace in Jerusalem.

From Easton's Bible Dictionary

Matthew George Easton, 1897

(Heb., or rather Egyptian, ahu, Job 8:11), rendered “meadow” in Gen. 41:2, 18; probably the Cyperus esculentus, a species of rush eaten by cattle, the Nile reed. It also grows in Palestine.

In Ex. 2:3, 5, Isa. 19:6, it is the rendering of the Hebrew suph_, a word which occurs frequently in connection with _yam; as yam suph, to denote the “Red Sea” (q.v.) or the sea of weeds (as this word is rendered, Jonah 2:5). It denotes some kind of sedge or reed which grows in marshy places. (See PAPER, REED.)

From Smith's Bible Dictionary

William Smith, 1884

There are two Hebrew words rendered "flag" in our Bible:

(1.) A word of Egyptian origin, and denoting "any green and course herbage, such as rushes and reeds, which grows in marshy places." (Genesis 41:2,18) (here translated meadow). It is perhaps the Cyperus esculentus .

(2.) A word which appears to be used in a very wide sense to denote "weeds of any kind." (Exodus 2:3,5; Isaiah 19:6)