INTELLIGENCE was taken from Latin. It appeared at about 1390, and was given the short and simple definition of “the faculty of understanding.”
The essential definition of FACULTY was “the power of doing anything.” About 1490/ a hundred years later, a second slightly expanded definition had been established.
INTELLIGENCE referred not only to the faculty of understanding but to “Understanding as a quality admitting of degree, specifically with reference to superior understanding, quickness of mental apprehension, and sagacity. “
The one that has had the most “reality” during modernist times: “INTELLIGENCE, in psychology, is the general mental ability involved in calculating, reasoning, perceiving relationships and analogies, learning quickly, storing and retrieving information, using language fluently, classifying, generalizing, and adjusting to new situations.”
At first take, this modern definition seems to cover just about everything necessary to describe intelligence and say that it exists as such. But it does not. The word “understanding” is not even mentioned in it.