Etymology: Middle English, from Old English mǣst; akin to Old High German meist most, Old English māra more — more at more
Date: before 12th century
1. greatest in quantity, extent, or degree <the most ability> 2. the majority of <most people> II. adverb Date: before 12th century 1. to the greatest or highest degree — often used with an adjective or adverb to form the superlative <the most challenging job he ever had> 2. to a very great degree <was most persuasive> III. noun Date: 12th century the greatest amount <it's the most I can do> IV. pronoun Usage: singular or plural in construction Date: 13th century the greatest number or part <most become discouraged and quit> V. adverb Etymology: by shortening Date: circa 1584 almost <we'll be crossing the river most any time now — Hamilton Basso> Usage: Although considered by some to be unacceptable in all cases, most is often used to mean “almost” in both spoken and, to a lesser extent, written English to modify the adjectives all, every, and any; the pronouns all, everyone, everything, everybody, anyone, anything, and anybody; and the adverbs everywhere, anywhere, and always. Other uses of this sense of most are dialectal.
New Collegiate Dictionary. 2001.