Inclined to droop, wilt, or lose energy; lethargic, weak, or lacking in vigor.
From Old Norse flag (to droop, flap, or flatter) combined with the adjectival suffix '-y', indicating a quality or characteristic.
The Old Norse root 'flag' is also the origin of 'flagrant' and relates to fluttering motions—whether it's a flag drooping in calm air or a person's energy drooping, the image is of something losing its upright vigor.
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