noun which may take the genitive case particle 'no', na-adjective
Describes something roughly the size of a human palm; used for small objects, devices, or creatures. Often appears in compound nouns like 掌大の本 (a palm-sized book).
He took a palm-sized notebook out of his pocket.
The tiny robot runs around on the desk.
Compound of 掌 (palm) and 大 (size), literally 'palm-sized'. The reading しょうだい follows standard on'yomi. The word is not extremely common but is transparent in meaning.