The process or practice of frequenting dells or small valleys, or behaving in a carefree manner in natural settings (rare).
From 'dell' (a small valley, from Old English 'dell' meaning 'pit' or 'hollow') plus the gerund suffix '-ing.' This usage is extremely rare and mostly found in 19th-century romantic literature.
This word almost certainly doesn't appear in modern dictionaries—it's exactly the kind of poetic non-word that Romantic poets might invent, then disappear when the movement faded.
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