Final answer:
Based on the context clues in the reading, 'gaslight' means tricking a person into believing they are insane.
Step-by-step explanation:
Based on the context clues in the reading, the definition of 'gaslight' is tricking a person into believing they are insane. The passage talks about how gas is looming through the fog and how the shops are lighted two hours before their time, giving the gas a haggard and unwilling look. This description suggests that the gas is manipulating the perception of reality, making someone feel as if they are going insane.