What is the origin of the word "genius"?

Search: genius origin

Why: In Nicholas Nickleby:

The figure looked at the bold Baron of Grogzwig for some time, and then said familiarly,
"There's no coming over you, I see. I'm not a man!"
"What are you then?" asked the baron.
"A genius," replied the figure.
"You don't look much like one," returned the baron scornfully.
"I am the Genius of Despair and Suicide," said the apparition. "Now you know me."

That doesn't really make sense in the context of what I understand a genius to be.

Answer: Get ready to learn:

Latin genius originally meant ‘deity of generation and birth’. It came ultimately from the Indo-European base *gen- ‘produce’ (source of English gene, generate, genitive, etc).

It broadened out considerably in meaning, initially to ‘attendant spirit’, the sense in which English originally acquired it. French took it over as génie - a word which, because of its phonetic and semantic similarity to Arabic jinn, 18th-century translators of the Arabian nights eagerly adopted into English as genie.

Ah, yes. Genie!

The main modern English sense, ‘person of outstanding intellectual ability’, which dates from the 17th century, goes back to a comparatively rare Latin ‘intellectual capacity’.

Genial (16^th c.) comes from Latin geniālis, a derivative of genius, which again originally meant ‘of generation and birth’ (a sense which survived into English: ‘And thou, glad Genius! in whose gentle hand the bridal bower and genial bed remain’, Edmund Spenser, Epithalamion 1595). It later developed in Latin to ‘pleasant, festive’.

Source: Word-Origins

The More You Know: I have no idea what's going on in that book. I feel like a genious playing the Trivial Pursuit Genius Edition.