mortar
臼 centers on a mortar: a sturdy bowl-shaped vessel used for grinding or pounding, especially in traditional grain processing.
臼 is a pictograph of a mortar, with the modern form showing the hollow interior and the two side walls.
The shape looks like a mortar with its hollow center and two side walls. Picture grains being pounded inside.
For キュウ, imagine a mortar so old it's been used for a 'queue' of generations: queue -> キュウ, and the mortar keeps grinding.
millstone; mortar
dislocation
molar (tooth); grinder; premolar
stone mortar; millstone; quern
tea grinding mortar (hand mill)
upper millstone
lower millstone; nether millstone
subluxation
congenital dislocation of the hip; developmental dysplasia of the hip
six-year molar
premolar
stone hand mill
mortar
molar
acetabulum; cotyloid cavity
acetabular roof
premolar
horizontal stone hand mill
molar
quern; hand mill