***** NOT A TEACHER *****
Hello, Devi_Dwi_Rahayu:
About two years ago, I found some definitions that really helped me. May I share them with you?
IDIOM
1. The words are NOT literal.
a. "To kill two birds with one stone."
b. It does NOT actually mean to kill two birds with one stone.
c. (My note) It means to do two things at the same time.
i. (My example) If I walk to the supermarket, I kill two birds with one stone. That is to say, I (a) get some food that I need and (b) I get some exercise.
d. An idiom can often change tense (my examples):
I will kill two birds with one stone by walking to the supermarket tomorrow.
I killed two birds with one stone yesterday by walking to the supermarket.
PROVERB
1. The words are usually literal. (They mean exactly what they say)
a. "An apple a day keeps the doctor away." (My note: If you eat an apple every day, it will be good for your health. Then you will not become sick and not have to go to a doctor.)
b. Usually you canNOT change the tense. (My note: It is no longer a proverb if you say, "An apple a day kept / will keep the doctor away.")
c. It is usually a complete sentence.
d. A proverb usually reflects folk wisdom. (My note: "Folk wisdom" refers to ideas that people have developed about life.)
James
Those definitions come from Lexicographic Description of English (1986) by Morton and Evelyn Benson. I found it in the "books" section of Google.