New words arise in several ways. They can be invented, imported from another language, made by mistake, or made by adding to, subtracting from, or mutating an existing word. And sometimes words attain a new meaning just by waiting a while.
The technical term for this last phenomenon is catachresis, though the word has other meanings, as we will see. The word catachresis arrived, through the Latin word of the same spelling, from the Greek katakhrēsis, excessive use, from katakhrēsthai, to misuse or use up. Its plural is catachreses, its adjectival forms catachrestic and catachrestical.
Whether or not words formed by catachresis are, strictly speaking, new words depends on how strict you are about such categorisation. Some authorities describe catachresis as the deterioration of a word, but it can also be described more neutrally as semantic drift, which is an inescapable characteristic of any language. As Robert Burchfield wrote in The English Language:
it is best to assume . . . that no single word in the [English] language is a stable, unchanging, and immutable legacy from the past, however fixed, dependable, and definable it may seem at any time.
In Our Language, Simeon Potter illustrates catachresis by reporting that when King James II saw the new St. Paul’s Cathedral, designed by Sir Christopher Wren, he described it as amusing, awful, and artificial. The King meant no offence, and presumably none was taken, because those words then denoted pleasing, awesome (i.e. awe-inspiring), and skilfully achieved, respectively. (Note: according to some sources it was Queen Anne who offered the now-puzzling observation.) When Chaucer used nice it meant ignorant or unaware; later it meant fastidious or precise, among other things – the OED has 14 separate entries for the word, differentiated by meaning and historical usage.