Seek everywhere, hunt for in all possible places. Oddly enough, high and low has a very old and quite different meaning, that is, designating people of all social conditions, high-born as well as low-born. This sense dates from about 1200; Shakespeare used it in The Merry Wives of Windsor (2.1): “He wooes both high and low, both rich and poor, both young and old.” In the current cliché, high and low refers simply to location, as in “I’ve looked high and low for the key and can’t find it anywhere.”