Definition of gnomon in US English:



  • 1The projecting piece on a sundial that shows the time by the position of its shadow.

    • ‘The problem is that the gardeners have been caught on the gnomon of their own sundial.’
    • ‘To ensure that the sundial registered roughly the correct time all the year round the gnomon had to be set at exactly the correct angle.’
    • ‘He placed a pole perfectly upright in the ground to make a simple sundial, or gnomon.’
    • ‘He also probably introduced the gnomon (a perpendicular sun-dial) into Greece and erected one in Sparta.’
  • 2Geometry
    The part of a parallelogram left when a similar parallelogram has been taken from its corner.

    • ‘Revolve the gnomon about its vertex and it can draw a circle; combine two gnomons and they form a square.’
    • ‘When the gnomon is turned up, it can measure height; when it is turned over, it can measure depth and when it lies horizontally it can measure distance.’


Mid 16th century: via Latin from Greek gnōmōn ‘indicator, carpenter's square’ (related to gignōskein ‘know’).