Final answer:
The dictionary definition of 'interpose' as it is used in the passage is 3) to put in a remark or question in the midst of a discourse.
Step-by-step explanation:
The dictionary definition that best reflects the word 'interpose' as it is used in the passage is number 3: 'to put in a remark or question in the midst of a discourse.'
In the passage, the younger man interrupts the lawyer while he is speaking. This interruption can be seen as the younger man 'interposing' with his own remark or question. This definition aligns with how the word is used in context.