The term 'Big Stream' can be solved by the word 'RIVULET', which is a seven-letter word. A RIVULET is a small stream or brook, typically one that is shallow and flows quickly. It is usually smaller than a river and may be ephemeral, flowing only during certain times of the year. Rivulets are often found in mountainous areas, where they form from melting snow or ice. They can also form from rainfall runoff or from groundwater seeping to the surface.