More prone to quick, restless movements; more fidgety or easily distracted.
From 'frisky' → 'flisk' with comparative '-er' (Old English 'ora'), the standard comparative ending for short adjectives.
English has two ways to make comparatives—short words get '-er' (faster, bigger, fliskier) while longer words get 'more' (more beautiful, more intelligent)—and the cutoff is usually around two syllables, a pattern that developed to make speech easier and faster.
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