To tremble uncontrollably due to fear, nervousness, cold, or intense emotion.
This simile dates to the 16th century and compares human trembling to the way leaves quiver in the wind. The comparison highlights both the involuntary nature of the shaking and its visibility to others, as leaves are easily observed moving even in light breezes, just as emotional or physical trembling is often noticeable to observers.
The leaf comparison is particularly apt because both human trembling and leaf movement are responses to external forces beyond conscious control - wind for leaves, and adrenaline or emotion for humans. Interestingly, the phrase has remained unchanged for centuries while many other nature-based metaphors have evolved, suggesting its perfect capture of the trembling experience.
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