temperamental

Temperamental is an adjective used to describe a person, animal, or thing that shows marked variability in mood, behavior, or performance. When applied to people, it often implies moodiness, irritability, sensitivity, or unpredictability; when applied to objects or systems, it suggests that performance depends on conditions or may fail under stress.

In everyday language temperamental can be pejorative, implying unreliable or difficult to work with. In clinical or developmental contexts, it may be used descriptively to indicate a temperament—a relatively stable pattern of emotional and arousal responses that is typical of an individual, though it may appear variable in particular situations.

Etymology: the term derives from the broader notion of temperament, the set of emotional and behavioral traits that characterize an individual. The suffix -al forms an adjective indicating relation to that stem. Over time, temperamental has extended to describe things whose behavior seems to be governed by temperament-like fluctuations rather than by fixed rules.

See also temper, temperament, moodiness, volatility. Temperamental is often contrasted with terms implying steadiness or consistency, such as reliable or stable. Usage varies by context; care is advised to avoid stigmatizing descriptions of people.