Datum
Datum , noun
[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.
Any writer, therefore, who... furnishes us with data sufficient to determine the time in which he wrote.
2.
a single piece of information; a fact; especially a piece of information obtained by observation or experiment; -- used mostly in the plural.
3.
(Mathematics) The quantities or relations which are assumed to be given in any problem.
4.
(Surveying) a point, line, or level surface used as a reference in measuring elevations. — RHUD
Collocations (1)
Datum line (Surveying) , the horizontal or base line, from which the heights of points are reckoned or measured, as in the plan of a railway, etc.