Old English heahweg "main road from one town to another;" see high (adj.) in sense of "main" + way (n.). High street (Old English heahstræte) was the word before 17c. applied to highways and main roads, whether in the country or town, especially one of the Roman roads. In more recent usage, it generally is the proper name of the street of a town which is built upon a highway and was the principal street of the place. Highway robbery is from 1707; as a trivial expression for something too costly, 1886.