A fuzzy fellow without feet
velvet, dun, plush
Dickinson piles up fabric words for the caterpillar's fuzzy body. **Dun** means dull grayish-brown—the exact color of many caterpillar species.
descend in plush
Caterpillars drop from trees on silk threads when disturbed. She describes the thread-dropping as a gentleman descending in fancy fabric.
damask residence
**Damask** is woven patterned silk. The chrysalis isn't actually silk (moths make silk cocoons, butterflies make hard chrysalises), but Dickinson treats the entire transformation as fabric work.
A feather on each shoulder
She's describing butterfly wings as fashion accessories—shoulder ornaments like military epaulettes or decorative plumes.
yelept
Archaic past participle of 'clepe' (to call or name). Deliberately old-fashioned diction—she's being playfully formal about scientific naming.