Oh man. This may prove to be a hard question to answer but I will try to give some examples of each which will hopefully demonstrate both their use and meaning.
Mentality = a particular way of thinking
1. I love learning languages, unlike some Americans who have a crappy attitude and a "This is America. Speak English." mentality. Instead, I see the value in learning the languages and cultures of other people and consequently becoming a more well-rounded person in the end.
2. He criticizes filmmakers for their blockbuster mentality. = He criticized filmmakers for thinking only about making movies that
could be blockbusters.
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Mind-set = a particular way of thinking : a person's attitude or set of opinions about something
1. He visited several locations in Massachusetts and spoke with residents to get a better understanding of their mind-sets.
* Here it means to get a sense of what their opinions are on various topics and how they think. Are they interested in jobs more? In bringing soldiers back from overseas? Human rights?
2. Understanding the complex mind-set of drug addicts will be crucial to the successful operation of such programs.
* If you don't take into consideration their attitudes on various components of a program, their rehabilitation isn't going to be successful.
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Mind = the part of a person that thinks, reasons, feels, and remembers
1. It is important that you keep your mind active as you get older to prevent Alzheimer's disease. One way to achieve this is to study another language.
2. His mind was full of holes from all those years of doing drugs. He really could not remember much.