n. 一茶匙的容量

[ noun ]
as much as a teaspoon will hold
<noun.quantity>

Teaspoonful \Tea"spoon`ful\ (t[=e]"sp[=oo]n`f[.u]l), n.; pl.
{Teaspoonfuls} (t[=e]"sp[=oo]n`f[.u]lz) or {Teaspoonsful}.
As much as teaspoon will hold; enough to fill a teaspoon. In
cooking, it is usually estimated as 4.9 milliliters, which is
1/6 of a fluid ounce, or 1/3 of a tablespoonful. In cooking
recipes it may be abbreviated as t.

Note: In the 1890 dictionary, it was defined as a fluid dram
or one quarter of a tablespoonful.
[1913 Webster +PJC]