datum

‖n.; pl. Data [ L. See 2d Date. ] 1. Something given or admitted; a fact or principle granted; that upon which an inference or an argument is based; -- used chiefly in the plural. [ 1913 Webster ]

Any writer, therefore, who . . . furnishes us with data sufficient to determine the time in which he wrote. Priestley. [ 1913 Webster ]

2. a single piece of information; a fact; especially a piece of information obtained by observation or experiment; -- used mostly in the plural. [ PJC ]

3. pl. (Math.) The quantities or relations which are assumed to be given in any problem. [ 1913 Webster ]

4. (Surveying) a point, line, or level surface used as a reference in measuring elevations. RHUD [ PJC ]

Datum line (Surv.), the horizontal or base line, from which the heights of points are reckoned or measured, as in the plan of a railway, etc. [ 1913 Webster ]