noun
freezing weather; cold weather
Literary or somewhat formal term for very cold weather; in everyday speech 寒い天気 is more common.
この寒天の中、外で待つのはつらい。
It's tough waiting outside in this freezing weather.
noun
agar-agar; vegetable gelatin
A jelly-like substance made from seaweed, used in Japanese sweets and cooking.
寒天を使ってゼリーを作った。
I made jelly using agar-agar.
From Chinese 寒天 (hántiān, 'cold weather'). The food sense arose in Japan from the resemblance of the solidified substance to frozen water.