...his sense of being in an unfamiliar place, affected his powers of coordination, always weak, and he began to dither slightly, caught his foot against one of the legs of the bed, opened his arms to save his balance and so let fall his parcels.
-- Barry Unsworth, Mooncranker's Gift, 1973
You make mistakes, don't you--dither, get things wrong…?
-- Penelope Lively, Pack of Cards, 1978-86
Dither entered English in the 1600s. It's a phonetic variation of the Old English didder, though its ultimate origins are unknown.