Animal that has 4 legs, e.g. a horse.
The way things are defined based on what you can observe rather than what you can measure, e.g. the colour, smell, or taste something is a qualitative definition.
The way things are defined based on what you can measure, e.g. how hot something is can be measured according to its temperature, and so is a quantitative definition.
A unit of energy according to the quantum theory, usually referring to the radiation or absorption of energy. Quanta (the plural of quantum) can be of different sizes. (See also Quantum theory.)
A theory (an idea with is not yet proven to be true) that energy is radiated and absorbed in units called quanta. According to the theory, the size of these quanta (E) is defined by the equation E = hυ (in which h is a constant, called Planck’s constant, and υ is the frequency of the radiation). (See also Quantum.)
Very common mineral found in the earth’s crust, consisting of silica (silicon dioxide, SiO2). Often found as extremely hard crystals which can be colorless and transparent when they are very pure.
An old-fashioned name for the liquid-metal element mercury. (See also Mercury.)
Edible fruit of a small tree or shrub, very similar to an apple but usually too sharp (or acidic) to eat. Not often used nowadays, but sometimes made into jam.
Compound known as an alkaloid extracted from the bark of the South African Cinchona tree. Inhibits the reproduction, in the human body, of parasites that cause the disease malaria. Was widely used to treat malaria in the 19th and early 20th centuries, and was particularly taken as a prophylactic (something that prevents a disease). Has now largely been replaced with more effective anti-malarial drugs. (See also Alkaloid.)