Английский Этимологический словарь - most

- O.E. mast "greatest number, amount, extent," earlier mжst, from P.Gmc. *maistaz, superlative form from Gmc. root of O.E. ma, mara (see more). Original sense of "greatest" survives in for the most part. Double superlative mostest is 1885, from U.S. Southern and Black English.