delta

Everyday

1. A flat, often triangle-shaped area of land where a river splits into many smaller streams before it flows into the sea, made from mud and sand the river carries. tree →
2. The fourth letter of the Greek alphabet, Δ or δ. tree →
3. In maths and science, Δ can stand for a change in an amount. tree →

In the lessons

In geography, deltas form at the mouths of rivers like the Nile and the Mississippi; the soil is rich for farming but floods easily. In maths and science, Δ means «change in». Phrases: «river delta», «the Nile Delta».

Examples

• The Nile Delta is shaped like a triangle. tree →
• The river drops its mud and sand to build a delta. tree →
• Many birds live in the wetlands of the delta. tree →
• Farmers grow rice on the delta because the soil is rich. tree →
• The Greek letter delta looks like a triangle: Δ. tree →
• Floods are common on a low, flat delta. tree →

Note

Countable: deltas. Named after the Greek letter Δ because many deltas are triangle-shaped. Not every river has a delta; strong waves or tides can wash the mud away.