From BiblePortal Wikipedia

Charles Buck Theological Dictionary [1]

A good or evil spirit or daemon, who the ancients supposed was set over each person to direct his birth, accompany him in his life, and to be his guard. Genius signifies that aptitude which a man naturally possesses to perform well and easily that which others can do but indifferently, and with a great deal of pain.

Cyclopedia of Biblical, Theological and Ecclesiastical Literature [2]

in Roman mythology. The belief in invisible protecting spirits, or beings who care for the welfare of single persons, is found among many people and nations, but nowhere was the doctrine of genii so perfect as in Rome; there there was a distinct belief in deities, who were given to every man from the time of birth. These deities were worshipped partly on general festive days, partly each for himself. Thus a genius was especially a protecting spirit of man. This belief extended still further; every important work and object had its genius or genii.