observable

Etymology

observe + -able

adj

1. Able to be observed.
   The strange new star was at the edge of the observable universe.
   In 1913, in the same year that Mother's Day became a nationally observable holiday, the American people passed another milestone: for the first time in American history more than one person in one thousand was divorced. 2004, John Lukacs, A New Republic: A History of the United States in the Twentieth Century
   Although intellectual property rights, such as patents, are highly observable, they are mostly limited to product technologies. Process technologies, or the routines endemic in the firm's production, are not readily observable, and thus cannot be easily imitated. 2008, David J. Teece, Technological Know-how, Organizational Capabilities, and Strategic Management
2. Deserving to be observed; worth regarding; remarkable.

noun

1. (physics) Any physical property that can be observed and measured directly and not derived from other properties
   Temperature is an observable but entropy is derived.
   In quantum mechanics, observables correspond to Hermitian operators. Also, they act a lot like random variables. Taking their expected value one may recover something resembling a classical observable.