Why do you say 'a one-way ticket' and not 'an one-way ticket'?

When to use "a" or "an"... this is one of the more complicated things in English grammar. 

A banana, a house, a penguin... 

An apple, an igloo, an elephant... 

The basic rule is, we use "an" instead of "a", to seperate vowels. We don't say "a elephant", we say "an elephant", to seperate the a from the e. 

HOWEVER... 

so then why wouldn't we say "an one way ticket"? Well... we only seperate vowels in a phonetic sense... phonetic, as in, what the word sounds like, rather than how it is spelled. 

"one way ticket" may start with the vowel O... but it it sounds like "Wun way ticket"... a "W" sound... 

We don't say "a ostrich"... we say "an ostrich"... because the O in "ostrich" is pronounced as a vowel... but the O in "one" is pronounced as the consonant "w". 

Make sense? No, of course it doesn't, English is just ridiculous sometimes. 

Technically, we are also (sometimes) supposed to use "an" instead of "a" before a "h", even though h is not a vowel. As in, "it would be an honor..." We don't say "an house", we say "a house". When it is a silent "h", we are supposed to use "an"... 

I'm so glad I grew up with this language, because I'd hate to have to learn it at school...

https://answers.yahoo.com/question/index?qid=20140815053933AALXVQh