Flag

Smith’s Bible Dictionary · William Smith, F. N. Peloubet, M. A. Peloubet

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

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 .
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)

In other dictionaries

William Smith; revised by F. N. Peloubet and M. A. Peloubet; CrossWire SWORD module Smith 1.3

Bible Strong digital edition from CrossWire module 1.3, based on the 1884 Peloubet revision with later digital enrichments preserved