To wander beyond proper bounds; to behave or speak excessively; to move or flow outside of normal limits.
From Medieval Latin 'extravagari' (to wander beyond), from 'extra' (outside) + 'vagari' (to wander), literally describing the act of straying beyond expected boundaries.
This verb is rare in modern English, but it perfectly captures what happens when something—an idea, a person, a fluid—moves beyond where it's supposed to stay, and 'extravasate' (blood flow) is a medical cousin of this verb.
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