drop

1

In Scotland, various units of mass, all 1/16th of an ounce:

In Scottish troy weight, for gold and silver, = 1/192 of a troy pound, about 1.944 grams; for various other commodities, = 1/256 of a troy pound, about 1.928 grams.

In Scottish trone weight, ¹⁄₃₂₀th of a trone pound, about 1.928 grams (about 29.75 English troy grains).

2

In English, a measure of capacity used in cooking and medicine. It has no definite volume. The size of a drop depends on such factors as the nature of the liquid, the material from which the dropper is made (does the liquid “wet” that material?), the dimensions of the dropper, the pressure on the liquid, any movement of the dropper, and other factors.

In dispensing medicine, these variables are controlled to some extent by supplying a specific dropper with the pharmaceutical. Obviously, the patient should not substitute a different medicine dropper.

For research on the sizes of drops, see this page.