indefinite article - Some words starting with vowels, preceded by 'an' instead or 'a'

We've all been taught in primary school how we're supposed to use 'an' instead of 'a' when we talk about an object whose name starts with a vowel, in its singular form.

-> An Apple
-> An Ostrich
-> An Elephant

But when we refer to one university, universe or even adjectives like useless, we use 'a' instead of 'an'.

-> A University
-> A Useless Boy
-> A Unique sight

Why is that so ? I get the fact that we use 'an' for words which start with consonants occasionally, for words like 'Hour','Honor', because the 'H' is silent. But what of the exceptions in the case of words starting with A,E,I,O,U ? Or is the just for certain words that start with 'U' ?

Answer

OALD on 'vowel':

a letter that represents a vowel sound. In English the vowels are a, e, i, o and u.

This is clear.

But then, the articles 'a' or 'an' depends on 'how do we pronounce' the words.

Now, your concern of why do those words take an indefinite article 'a' and not 'an'.

Check this:

Use 'A' before words such as "European" or "university" which sound like they start with a consonant even if the first letter is a vowel. Also use 'A' before letters and numbers which sound like they begin with a consonant, such as "U", "J", "1" or "9". Remember, it is the sound not the spelling which is important. For example, "1" is spelled O-N-E; however, it is pronounced "won" like it starts with a "W".

Examples:

She has a euro (sounds like "yu-ro")
That number is a "1" (sounds like "won").

So, because of their consonant sound we use 'a' instead of 'an'.

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University is 'यूनिवर्सिटी' and there you have 'यू' to pronounce. It is not pronounced with vowel a(अ), e(ए), i(ई,आई), o(ओ), or u(अ).