1) As a word meaning to waylay, or take up a position in order to ambush somebody.
The history of ‘forestall’ can be traced back over one thousand years. In those earliest examples the element ‘stall’ simply meant place or position. Later, it was produce that was ‘ambushed’ or intercepted, on its way to the public markets, and to ‘forestall’ came to signify the buying up of goods before they reached the market. An Act in 1353 made this practice illegal and its repercussions are evident in courts of various kinds throughout the following centuries: 1408 Excepto quod, si aliquis legitimo modo per xij juratos fuerit convictus forstallarius, Beverley. In 1485, the poulterers in York were ordered to sell there pulan in noo place but in the common market called Thursday market and not in noo housses … and goo not from bar to bar to forstall any vitall that cometh to the market. In 1589, a baker named William Fell was indicted for buyeng … malt, and selling the same agane contrary to the statute maid against forstallers and ingrossers, York. In view of the word’s earliest history, the ‘stall’ is unlikely to have had anything to do with stalls in the market, at least directly, but our ancestors may have made such a connection.