Of or pertaining to a trigon (trigon, n. 3a). Also as n., short for trigonal instrument. Obsolete. rare.

Something that inclines (in various senses), or that causes something to incline. rare.

spec. The flat surface of a sundial or similar device, upon which the shadow falls and on which the dial is drawn. Also called dial-plane.

A triangular instrument used in surveying; also, one used in dialling. Obsolete.