Englishfor English speakers
a
Determinative
—
A is used when the following word could be any of a certain type.
Compare "A book I saw on the shelf" and "The book I gave you yesterday".
a
Noun
—
A is the first letter of the alphabet.
The letter "a" comes before "b".
—
In some schools, an A is a very high grade.
Ron got an A on his earth science test.
real
Adjective
—
A thing that is true is real.
Strange as the story sounded, the story was real.
—
Something that is not artificial is real.
The nice shoes were of real leather.
dead
Adjective
—
Not alive.
My brother is dead. His funeral was last week.
—
Without power.
The problem is a dead battery.
—
Without feeling, numb.
My arm is dead. I cannot feel it.
dead
Adverb
—
Exactly, completely.
He thinks you are a woman, but you are a man. He is dead wrong.
one
Determinative
—
(ordinal first) The number 1.
We have one nose and one mouth.
one
Noun
—
The number 1.
One is the smallest whole number.
one
Pronoun
—
One is a singular pronoun which means "someone" or "people". It is used more often in formal writing.
It is easy to see the difference if one looks closely enough.