Where it comes from
The acorn is a twentieth-century English and Danish catalogue name for a bowl that looks like the nut: full at the heel, tighter at the rim. It sits next to the apple in old lists. Danes later made it slimmer. It is not a Dublin (the Dublin opens at the top) and not a tomato (the tomato is flat). There is no famous inventor; there is a drawing everyone recognised.
The specification
Bowl: rounded, pinching toward the rim. Shank: usually straight or lightly bent. 469/25 is the acorn in this cabinet: rusticated dark, ruby acrylic stem, gold stem mark, 2025 archive. No millimetres on the plate. The chamber still has to be even; the pinch is the outside line.
Next to the apple
If you like a round bowl that does not open as wide as 419/24’s tomato and does not stay as spherical as 423/24’s apple, the acorn is the word. One serial on this site. Write with 469/25 if that plate is the one you mean.