"I'm supposed to meet friend in 1 hour" what does this sentence exactly means and what is the role of the word "suppose" here.
If you look up "suppose" by itself, you will get nowhere with this sentence; the words be supposed to must be treated as a unit. To "be supposed to" generally means that you are intended, expected, or obligated to do something:
Definition of be supposed to (from merriam-webster.com):
1: to be expected to do something:
- They are supposed to arrive tomorrow.
- She was supposed to be here an hour ago.
- The movie was supposed to earn a lot of money at the box office, but it didn't.
2: to be intended or expected to be something
- The party was supposed to be a surprise.
3 —used to show that one is angry or offended by something
- Was that supposed to be funny? I thought it was quite rude.
- “Well, you've done it again.” “What's that supposed to mean?”
4 —used to say what someone should do
- You are supposed to listen to your parents.
- I'm supposed to clean my room before I go outside.
- What are we supposed to do in a situation like this?
- Do what you're supposed to.
5 —used to refer to what someone is allowed to do
- We were not supposed to leave the room.
- Are you supposed to be here after the building has closed?
6 —used to indicate what people say about someone or something
- “I heard that she's good.” “She is supposed to be the best doctor in town.”
- That breed of dog is supposed to be good with kids.
- The word is supposed to be derived from Latin.
In your sentence, the intended meaning is clearly 1), your friends are expecting you to be there to meet them (and there will probably be some disappointment or problems if you do not).
"I suppose that I will meet my friend" means I believe that we are going to meet - but it has not (yet) been proven to be true. (We'll only know that we are definitely going to meet once we actually meet).
Really, it's shorthand for "I (believe that I have arranged that I) am going to meet my friend".
"I am supposed to meet" means that my friend is the one who believes that we will meet, ie my friend believes that we have arranged to meet. Probably because my friend and I discussed and agreed the meeting, and I have not agreed a change to that arrangement with my friend.
From the British Council's grammar web-site:
"We use present tense forms after phrases like what if, in case and suppose to talk about the future if we think it is likely to happen"