The superlative form of 'chirk,' meaning the most cheerful, lively, or characterized by chirking sounds.
From 'chirk' plus the superlative suffix '-est.' This follows the standard formation of superlatives for short adjectives in English (like brightest, fastest, loudest).
Superlatives with '-est' are one of the oldest parts of English grammar, unchanged from Old English—you can feel how ancient this pattern is when you say 'oldest' or 'fastest,' words that have sounded essentially the same for over 1,000 years.
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