Unfortunately, there is no such dictionary that defines all of these terms. I think the reason for that is that many of the words on the LSAT take on context-dependent meanings. As you continue to practice, you will eventually run into more and more different usages of all these words.
Evidence is anything used to support a point. As for primary evidence, I am honestly not sure as I don't think I have consciously seen this usage. I can only imagine that this means this was the main support for the argument, but I would be interested to see the specific question that used this.
Inference is something that has to be true based on the information provided in the passage. You can infer it from the passage.
Three restaurants open tonight. Chinese, Italian, and Ethiopian. We are going to one of these three restaurants tonight. The Ethiopian and Italian restaurants are fully booked. Therefore, we are going to the Chinese restaurant.
We are able to make this inference based on combining the facts presented.
Phenomenon is used to describe something that exists or occurs. Many things can be described as phenomenon, dependent on the context.
I would say that it would be best for you to keep practicing and noting when you feel that a word was used in an interesting or noteworthy way. Eventually you will see all the different variants and feel very confident when you run into these.
I hope this helped despite the vague answers!
nicolebetNovember 9, 2021
@Ben, arg structure, question 13 has 'primary evidence'