a long line of rocks or sand near the surface of the sea 礁；礁脉 
a coral reef 珊瑚礁 the Great Barrier Reef 大堡礁
a part of a sail that can be tied or rolled up to make the sail smaller in a strong wind 缩帆部；帆的可收缩部
Word Originnoun sense 1 late 16th cent. (earlier as riff): from Middle Low German and Middle Dutch rif, ref, from Old Norse rif, literally ‘rib’, used in the same sense. noun sense 2 Middle English: from Middle Dutch reef, rif, from Old Norse rif, literally ‘rib’, used in the same sense.