noun
tengusa; red algae (Gelidiaceae)
Refers to red algae of the family Gelidiaceae, especially Gelidium crinale. Commonly used to make agar (寒天).
テングサは寒天の原料として知られている。
Tengusa is known as a raw material for agar.
海岸でテングサを採集した。
We gathered tengusa on the shore.
寒天 is the processed agar jelly, while テングサ is the raw seaweed used to make it.
The origin of the name is uncertain. The kanji 天草 literally means 'heaven grass', but this is likely an ateji (phonetic) assignment.