“Human” and “rational” may apply to exactly the same individuals while presenting their meaning under different aspects. “Human” names the species; “rational” marks its intellectual distinguishing feature.
Thus equality of predication does not require synonymy or exactly matching definitions. It concerns extension, the set of individuals falling under each concept.
Zayd is human and rational.
Amr is human and rational.
No individual is human without being rational in this technical sense, and none is rational without being human within the intended classification.
Only when both universal directions hold is the relation equality.