Quantity - (Webster's 1828 Dictionary)
QUAN'TITY, n. [L. quantitas, from quantus, how much, or as much as.]
1. That property of any thing which may be increased or diminished.
This definition is defective, and as applicable to many other properties as to quantity. A definition strictly philosophical cannot be given. In common usage, quantity is a mass or collection of matter of indeterminate dimensions, but consisting of particles which cannot be distinguished, or which are not customarily distinguished, or which are considered in the aggregate. Thus we say, a quantity of earth, a quantity of water, a quantity of air, of light, of heat, of iron, of wood, of timber, of corn, of paper. But we do not say, a quantity of men, or of horses, or of houses; for as these are considered as separate individuals or beings, we call an assemblage of them, a number of multitude.
2. An indefinite extent of space.
3. A portion or part.
If I were sawed into quantities. [Not in use.]
4. a large portion; as a medicine taken in quantities, that is, in large quantities.
5. In mathematics, any thing which can be multiplied, divided or measured.
Thus mathematics is called the science of quantity. In algebra, quantities are known and unknown. Known quantities are usually represented by the first letters of the alphabet, as a, b, c, and unknown quantities are expressed by the last letters, x, y, z, _c. Letters thus used to represent quantities are themselves called quantities. A simple quantity is expressed by one term, as + a, or - abc; a compound is expressed by more terms than one, connected by the signs, + plus, or -minus, as a + b, or a - b + c. quantities which have the sign + prefixed, are called positive or affirmative; those which have the sign - prefixed are called negative.
6. In grammar, the measure of a sullable; that which determines the time in which it is pronounced.
7. In logic, a category, universal, or predicament; a general conception.
8. In music, the relative duration of a note or syllable.
Quantity of matter, in a body, is the measure arising from the joint consideration of its magnitude and density.
Quantity of motion, in a body, is the measure arising from the joint consideration of its quantity of matter and its velocity.