Principal fact
Black's Law Dictionary · Henry Campbell Black, M.A. · 1910
Black's Law Dictionary
In the law' of evidence. A fact sought and proposed to be proved by evidence of other facts (termed "evidentiary facts") from which it is to be deduced by inference. A fact which is the principal and ultimate object of an inquiry, and respecting the existence of which a definite belief is required to be formed.
3 Benth. Jud. Ev. 3; Burrill, Circ. Ev. 3, 119