How many words do you know which starts with vowel but we don't use "an" with them?

This is just a little riddle. Let's see how many words do you know.

Answer

"University"
"Useful"
"Use"
I know just these three words.

Answer2

altogether
as
an
at
a
arthritis
east
earth
uranus
uranium
eulogy
most words with "y"
yellow
yak
yoyo
yam
"all the plural forms of words starting with a vowel"

Answer3

an, in, a, on,

Answer4

a used (anything)

Answer5

an ...