what is the exact meaning of idiot? and how to prevent it?

Answer 1

The exact meaning of idiot is stupid.
If you call someone as idiot, you are showing that you think they are very stupid.eg. a bunch of idiot journalists are waiting to ask me stupid questions.
An idiot is a person who is mentally ill or mentally handicapped.
The later part of your question is not clear to me.

Answer 2

well in all technicality the word idiot was first used in ancient Greece, it was said that a person who did not vote was an idiot.. so America is full of a bunch of idiots.

Answer 3

One definition might be "An idiot is someone who doesn't know how to look up a word in the dictionary."

OK -- just kidding. Here is the definition from Webster:
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idiot[noun]

Entry Word:
idiot
Function:
noun

Text: a stupid person Synonymsblockhead, cretin, dodo, dolt, donkey, dope, dork [slang], dumbbell, dummy, dunce, fathead, goon, half-wit, ignoramus, imbecile, jackass, knothead, moron, nincompoop, ninny, nitwit, numskull (or numbskull), pinhead, simpleton, stock, turkey Related Wordsbooby, fool, goose, loony (also looney), lunatic, madman, nut, zany; loser; gawk; featherbrain, scatterbrain; beast, boor, cad, churl, clown, creep, cur, heel, jerk, skunk, snake, stinker, villain Near Antonymsegghead, intellectual, sage, thinker Antonymsbrain, genius