Step 1: Understanding the Question:
The question asks for the antonym (a word with the opposite meaning) of the word 'discipline'.
Step 2: Analyzing the Meaning of 'Discipline' in Context:
In the passage, 'discipline' refers to self-control, training, and a structured habit of choosing intellectually stimulating books. It implies order and regulation of one's reading habits.
Step 3: Finding the Opposite:
The direct opposite of control and order is a lack of control and order. The most common antonym for discipline is formed by adding the prefix 'in-', which negates the root word.
Therefore, the opposite is 'indiscipline'. Other possible words, depending on the context, could be 'chaos', 'disorder', or 'negligence'. However, 'indiscipline' is the most precise antonym.
Step 4: Final Answer:
The opposite word of 'discipline' is indiscipline.