Full of frets or worry; nervous and easily agitated; also in heraldry, a pattern filled with interlocking diagonal lines.
From 'fret' + the adjective-forming suffix '-y', which became productive in Middle English to create descriptive words from nouns and verbs.
Fretty is a perfect example of English's '-y' suffix creating personality descriptors—from 'fret' (the action) we get 'fretty' (the personality), just like 'chat' becomes 'chatty' and 'worry' becomes 'worrisome'.
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