Deliberately and intentionally, especially when doing something wrong or against the rules.
From Old English 'wilful,' meaning 'self-willed' or 'deliberate,' derived from 'will' (desire/choice) and '-ful.' The adverb form adds '-ly' to describe an action done with intention.
If you break something by accident, you're not responsible, but if you willfully break it, you knew exactly what you were doing. The law cares deeply about this distinction—it's the difference between a fine and serious punishment.
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