Step 1: Understanding the Concept:
The question pertains to Gordon Allport's trait theory of personality and seeks the specific term he used for a rare but all-encompassing personality trait.
Step 2: Detailed Explanation:
Gordon Allport categorized personality traits into a three-tiered hierarchy:
Cardinal trait (B): This is a singular, overarching trait that fundamentally defines an individual's life. People possessing such a trait are often primarily identified by it. Allport considered cardinal traits to be uncommon; not everyone exhibits one. Examples include Machiavellianism as exemplified by Machiavelli, or the profound compassion of Mother Teresa.
Central trait (A): These represent the core characteristics that form the foundational elements of personality. Every individual possesses a limited number of central traits (e.g., honesty, kindness, shyness) that would be suitable for inclusion in a letter of recommendation.
Secondary trait (D): These traits are narrower in scope and manifest only under specific circumstances or in particular situations (e.g., experiencing anxiety during public speaking).
Source trait (C) is a concept originating from Raymond Cattell's trait theory, not from Gordon Allport.
Step 3: Final Answer:
According to Allport, a single, dominant trait is referred to as a cardinal trait.