In Nicholas Nickleby, Dickens uses the word genius thirty-three times, using five out of the ten major senses of the word in the Oxford English Dictionary. There must be a deliberate playfulness in employing the word in so many of its meanings. Here’s a survey of the various senses employed:
Its boarding-houses are musical, and the notes of pianos and harps float in the evening time round the head of the mournful statue, the guardian genius of a little wilderness of shrubs, in the centre of the square.
This is sense 1a in the OED:
1.a. With reference to classical pagan belief: […] a guardian spirit similarly associated with a place, institution, thing, etc.
‘“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.”
This is sense 4:
4. Chiefly with of. A quasi-mythological personification of something immaterial (as a virtue, custom, institution, etc.)
‘I think I have caught it now,’ said Miss La Creevy. ‘The very shade! This will be the sweetest portrait I have ever done, certainly.’
‘It will be your genius that makes it so, then, I am sure,’ replied Kate, smiling.
This is sense 7b:
7.b. Natural ability or capacity; quality of mind; attributes which suit a person for his or her peculiar work.
‘Well, so it is,’ rejoined Crowl; ‘and I’ll tell you what’s more—I think these two geniuses, whoever they are, have run away from somewhere.’
This is sense 8b:
8.b. An exceptionally intelligent or talented person, or one with exceptional skill in a particular area of art, science, etc.
but Crowl is being sarcastic: he actually suspects Nicholas and Newman of being escaped felons of some kind.
‘’Gad, Nickleby,’ said Mr. Mantalini, retreating towards his wife, ‘what a demneble fierce old evil genius you are!’
This is sense 2:
2. Either of two mutually opposed spirits imagined as accompanying a person throughout his or her life and exerting either a good or bad influence. Hence in extended use: a person who exerts a good or bad influence over another’s character, conduct, or fortunes.