easywhat am-i

I start with the letter e, I end with the letter e. I contain only one letter, Yet I am not the letter e! What am I?
Common Wrong Answers
“Eagle”
An eagle starts with 'e' and ends with 'e', but it does not contain only one letter.
“Eye”
An eye starts with 'e' and ends with 'e', but it also does not contain just one letter; it refers to a part of the body.
“Egg”
An egg starts with 'e' but does not end with 'e', thus failing to meet the criteria of the riddle.