The correct answer is: an event that is repeated three times.
The example taken from Morte D'Arthur by Sir Thomas Malory refers to the final climax when Sir Bedivere throws the sword Excalibur into the lake and the Lady of the Lake extends her arm to take it and then shakes it three times before immersing into the water. The idea of shaking the sword three times is not a coincidence; an event that is repeated three times is a common symbol in medieval literature that is related to the concept of the Holy Trinity, it is both a Biblical and a mystical number that reflects the concept of perfection. It is linked as well with the Celtic symbolism since the number three is a magic number represented by the clover in the Druidic tradition.
