Past tense of chuckle; laughed in a quiet, happy, or slightly suppressed way.
From 'chuckle' (to laugh softly, from possibly onomatopoetic origins) plus '-ed' past tense marker, describing a lighter form of laughter.
The word 'chuckle' itself probably came from the sound people make when laughing quietly—it's onomatopoeia, where the word mimics the thing it describes, just like 'giggle' or 'chortle'!
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