1. noun /ˈvɜːtɪkəl,ˈvɝtɪkəl/
2. adjective /ˈvɜːtɪkəl,ˈvɝtɪkəl/
a) along the direction of a plumbline or along a straight line that includes the center of the Earth
b) In a two dimensional Cartesian co-ordinate system, describing the axis oriented normal (perpendicular, at right angles) to the horizontal axis.
Wikipedia foundation.