Third person singular present tense of gnaw; bites or scrapes with the teeth, or persistently worries or troubles.
From Old English gnagan, to bite or scrape. Gnaws is the modern conjugated form for he/she/it. The word has meant both physical biting and metaphorical worry for centuries.
A beaver gnaws through a tree trunk, but 'doubt gnaws at his mind'—English lets us apply gnaw to emotions, showing how metaphor helps us understand abstract feelings through physical sensation!
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