Lacking enthusiasm; showing indifference, coolness, or deliberate disinterest toward something.
From antienthusiast + -ic (adjective suffix). This describes the characteristic quality or attitude of being unenthusiastic.
A teenager's antienthusiastic response to their parents' jokes—that eye-roll and 'cool, dad'—is a classic sign of adolescent detachment, even if they secretly appreciate the effort.
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