Answer:
The word discipline is used to define the training that develops self-control.
Step-by-step explanation:
The word discipline is used as a noun in the given sentence. The word discipline is derived from the Latin word disciplina which means knowledge and instruction. As a noun, the word refers to the process of training that helps to develop self-control.
The given statement is talking about Chad's habit that he has developed through self-control. He has become disciplined in eating healthy food and exercising daily.
Therefore, the word discipline refers to the training that develops self-control.