Great diligence
Black's Law Dictionary · Henry Campbell Black, M.A. · 1910
Black's Law Dictionary
Such a measure of care, prudence, and assiduity as persons of unusual prudence and discretion exercise in regard to any and all of their own affairs, or such as persons of ordinary prudence exercise in regard to very important affairs of their own.
Railway Co. v. Rollins, 5 Kan. 180; Litchfield v. White, 7 N. Y. 438, 57 Am. Dec. 534; Rev. Codes N. Dak. 1899, § 5109