As a Noun: 1. A line that goes in a slanting direction. English = diagonal. 2. A diagonal line that separates letters, words, or numbers, especially a flat or apartment number from the building number. English = slash, stroke. 3. A slanting straight line that joins two opposite corners of a straight-sided shape such as a square or cube. English = diagonal. 4. A score in ten pin bowling in which all the pins are knocked down in two consecutive bowls. English = spare. As a Verb or Adjective: 1. To go in a slanting direction, as if joining two opposite corners of a straight-sided shape such as a square or cube. English = (be) diagonal.