_Abnormal._ Deviating from type. _Aborigines._ The inhabitants of a region, or, in some cases, the plants and animals, found by colonists. Literally, those that have been in the land from the beginning of things. _Abort._ Have premature delivery of a child. Remain undeveloped or sterile, or dwindle away. _Absolute._ Pure. The absolute, philosophically speaking, is final and total reality. _Absorption._ Disappearance through incorporation in something else. The solution of a gas in a liquid is called absorption. Rays of light may be absorbed in some mediums. _Abstract._ Theoretical, aside from particular instances. _Abulia._ Weakness of will. _Abyssal._ Relating to the depths of the sea. _Acaulescent._ Apparently stemless. _Acceleration._ Rate of increase of velocity per time unit. Rate of change of the velocity of a chemical reaction. The acceleration of a star is the time it gains daily over the sun. _Accident._ A property which is not essential to our conception of a subject. _Achene._ A small, dry, indehiscent, one-seeded fruit. _Achromatic._ Colorless, transmitting light without decomposing it. _Acid._ A substance that neutralizes and is neutralized by a base, and which contains hydrogen. A compound that produces hydrogen ions when it decomposes in aqueous solution. _Actinium._ A radioactive substance, believed to be an element. _Actinozoan._ One of a class of coelenterates including the corals. _Aculeate._ Having a sting, prickly. _Acuminate._ Tapering to a point. _Adiabatic._ Maintaining a constant temperature. _Adrenalin._ A crystalline substance obtained from suprarenal extract. _Adsorption._ The condensation of dissolved substances on the surface of a liquid or solid. _Adventitious._ Not in the usual place, as a root. _Aerial._ Atmospheric. _Affect._ Disease, emotional complex. _Afferent._ Conducting inward. _Agoraphobia._ The morbid fear of public places. _Agronomics._ The science of crop production. The scientific management of land. _Agrostology._ The study of the grasses. _Air._ The atmosphere, a gaseous substance of which oxygen and nitrogen are the principal constituents. _Air pump._ A pump for forcing air into, or taking it out of, hollow places. _Albino._ An animal, especially a human being, characterized by the congenital absence of coloring pigment in the skin, hair, and eyes. The typical albino has very light skin and hair and pink eyes. _Albumen._ A substance, usually edible, found between the skin embryo of seeds. _Albumin._ A class of proteids found in blood serum, milk, and muscle. _Alcohol._ Ethyl alcohol, the substance which causes intoxication, and a whole class of substances which are similar to it. They are hydroxides of organic radicals. _Alga._ Seaweed. Chiefly used in the plural: algae. _Alkali._ Caustic hydroxides which form soluble soaps with fatty acids and turn red litmus paper blue.