In a manner that makes a loud crunching sound, like biting something hard and brittle.
From 'craunch,' a dialectal English verb meaning to crunch or crush with the teeth, likely imitative in origin. The '-ing' suffix creates the present participle, and '-ly' converts it to an adverb. The word evolved in British English to describe the auditory experience of eating crunchy foods.
English has tons of onomatopoeia words like this that actually describe sounds we make while eating—'craunch' is the British cousin of 'crunch,' and it's delightfully specific about texture and noise at the same time.
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