To jump or to fit or unite with like a graft; as, both our
inventions meet and jump in one. Hence the adverb exactly,
“Good advice is easily followed when it jumps with our own ...
inclinations.” —Lockhart: Sir Walter Scott, chap. x. p. 241
The Scotch use jimp, as, “When she had been married jimp four
months” (The Antiquary.)
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894