cocoon
US /kəˈkuːn/
UK /kəˈkuːn/

1.
茧
a silky case spun by the larvae of many insects, especially silkworms, to protect themselves in the pupal stage
:
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The caterpillar spun a beautiful cocoon before transforming into a butterfly.
毛毛虫在变成蝴蝶之前,织了一个美丽的茧。
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The silkworm's cocoon is used to produce silk.
蚕的茧被用来生产丝绸。