The Hebrew noun achu (אָחוּ) refers to reeds, marsh grass, or water-loving plants — the kind of vegetation found in riverbanks and marshy areas of the Nile delta and similar environments. It is an Egyptian loanword or early Semitic borrowing, appearing in texts set in Egypt.
The word appears famously in Pharaoh's dream (Genesis 41:2) — seven fat cows grazing among the achu (marsh grass) along the Nile, followed by seven lean cows. Joseph's interpretation of this dream saved Egypt and the surrounding nations from famine, and ultimately preserved the family of Israel. The achu of the Nile thus forms the agricultural backdrop of one of Scripture's great stories of divine providence. Even the most ordinary details of landscape — marsh reeds by a river — serve as the setting for God's sovereign purposes.