When I use a word . . . . Defining with finesse

Abstract

The word for a definition in both Latin and Greek is a word meaning or derived from a word meaning a boundary. In Greek it is ὅρισμός (horismos) from ὅρος (horos), a boundary. The horizon is a kind of boundary, and a definition is limited by its horizon, the place beyond which no more meaning should be included. In Latin the word for a definition is finis, which also means a boundary. Five features characterise a good definition: it should describe all the essential attributes of the thing being defined, no more no less; it should avoid circularity, such as defining a medication error as an error in medication; it should be neither too wide nor too narrow; it should not use obscure terms that may themselves need definition; and it should be couched in positive terms, saying what something is, not what it is not. All of these apply as much to definitions of medical words as to any other kinds.