chinquapin, mallet, spine
椎 centers on a hard, rounded object used for striking or as a structural support: a mallet or hammer, and by extension the spine (vertebrae) which are like small mallets or blocks stacked together. The chinquapin tree meaning is a specific botanical application, likely from the tree's hard wood used for mallets.
椎 combines 木 (tree/wood) with 隹, which likely contributes the sound. The character originally referred to a type of tree (chinquapin) whose hard wood was used for making mallets, and later extended to mean mallet and spine.
The left side 木 is a tree, and the right side 隹 looks like a bird. Imagine a woodpecker (bird) hammering a tree with its beak like a mallet, or picture the tree's trunk as a spine with vertebrae stacked like little mallets.
For ツイ, imagine a mallet striking a tree and making a sharp 'tsui' sound: tsui -> ツイ, like the crack of wood being hit.
spine; vertebral column; spinal column; backbone
shiitake mushroom (Lentinula edodes); shitake
any beech tree of genus Castanopsis; chinquapin; chinkapin
cervical vertebrae
intervertebral disk
lumbar vertebra; lumbar vertebrae
vertebrate; vertebrates; vertebrata
thoracic vertebra; thoracic vertebrae
vertebra; vertebrae
Castanopsis sieboldii (species of chinquapin)
Castanopsis sieboldii (species of chinquapin)
spina bifida
spina bifida
sacral vertebra
Castanopsis cuspidata (species of chinquapin)
Temnospondyli; extinct order of tetrapods
Castanopsis cuspidata (species of chinquapin)
caudal vertebra
ankylosing spondylitis
Spina Bifida Association of Japan