swelled belly, dropsical, to swell, inflated
痮 centers on abnormal swelling or bloating, especially in the belly, often associated with dropsy or fluid retention. The idea extends to general inflation or puffing up.
痮 combines 疒 (sickness) with 長, which likely contributes the sound and the idea of something extending or swelling. The exact historical development is uncertain.
The sickness enclosure 疒 wraps around 長 (long), like a belly that has grown long and swollen from illness.
For チョウ, imagine a swollen belly that looks like a long, inflated balloon: a distinctive invented name "Chou" (pronounced choh) for the balloon cues チョウ, and the long balloon matches the 長 inside.