What is ZEQUUM ET BONUM? Definition of ZEQUUM ET BONUM in Black's Law Dictionary
"The Roman conception involved in cequum et bonum' or `cequitas' is iden- tical with what we mean by 'reasonable' or nearly S0.
"On the whole, the natural justice or 'reason of the thing' which the common law recognizes and applies does not appear to differ from the 'law of nature' which the Romans identified with jus gentium, and the medieval doctors of the civil and common law boldly adopted as being divine law revealed through man's natural reason." Sir F. Pollock, Expans. of C. L. 111, citing  2 Ch. 661, where jus naturale and cequum et bonum were taken to have the same meaning.
1Equum et bonum est lex legum. What is eq- uitable and good is the law of laws. Hob. 224.