dragonfly, millipede, lizard
蜓 centers on small, elongated creatures: dragonflies, millipedes, and lizards. The common thread is a long-bodied, many-legged or winged invertebrate or reptile.
蜓 combines 虫 (insect/reptile) with 廷, which likely contributes the sound. The character is used for small crawling or flying creatures, but the exact historical development is uncertain.
The insect radical 虫 on the left hints at a bug or reptile. The right side 廷 looks like a long, segmented body with legs, like a dragonfly or millipede stretched out.
For エン, imagine an enormous dragonfly with a wingspan as wide as the letter 'N' (en). The 'en' sound cues エン while the dragonfly hovers over the insect radical.
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Siebold's dragonfly (Anotogaster sieboldii); jumbo dragonfly