A dialectal or regional term that may refer to kidnapping or a sudden, unexpected seizure or capture.
Possibly combining 'guard' or 'garden' with 'nap' or dialectal elements; this appears to be a rare or regionally specific word with uncertain etymology.
Language contains thousands of regional words that virtually nobody uses anymore—gardnap might be one of those Yorkshire or Scottish dialect words that survived in old dictionaries but died out in actual speech!
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