Chapter 21:

acquit (vb.): clear of a charge; find not guilty
charged the jury (vb. + n.): When Judge Taylor charges the jury, he gives them instructions in law before they go off to deliberate or decide the case
exhilarated (adj.): cheerful, merry
indignant (adj.): angry

 

Chapter 22:

cynical (adj.): a cynic is someone who often belittles or makes fun of someone else. Aunt Alexandra tells Dill that his remarks about his own Aunt's drinking habits are cynical, especially
since, as a child, Dill should have more respect for his elders.
fatalistic (adj.): To be fatalistic about something is to accept the event as though it were inevitable; that is, that nothing could be done to change or alter it.
feral (adj.): wild; savage
heathen (adj.): unenlightened; without religion or morals
ruefully (adv.): regretfully

 

Chapter 23:

commutes (vb.): changes; makes less severe
dry (adj.): clever but subtle
furtive (adj.): sneaky
infantile (adj.): childish
statute (n.): law
vehement (adj.): full of emotion and strong feeling
wary (adj.): cautious
wryly (adv.): humorously; slightly sarcastic