Oh So Confusing! Yea Vs. Yeah Vs. Yay - What's the Difference?

Example of using 'yeah' and 'yay'
Many of us use slang when texting, social networking, or otherwise. The words yea, yeah, or yay are three words that are used very frequently, and sometimes, even interchangeably. Most of us aren't really aware of what these three words actually mean. If you too do the same, here's a Buzzle post that will help you understand these three words better and use them correctly.
In a Nutshell
Very briefly, yea is a formal yes or an affirmative vote, yeah is an informal yes, and yay is an exclamation.
The word yea originates from aye, both are ways of affirmation or saying yes. Although both were in frequent use prior to the 19th century, they're rarely used today. However, yea is still used by some authors in an archaic sense, or in a legislative (law-making) context where it is used to denote an affirmative vote.
'Yeah' basically originates from American English; however, it's used widely across the world. It is believed to have first appeared in writing somewhere in the first decade of the 20th century.

Lastly, yay came into use somewhere in the 1940s, and gained popularity post 1970. Given below is a comparison between yea, yeah, and yay, highlighting their meanings, pronunciation, and examples of each. Take a look!
Difference Between Yea, Yeah, and Yay
Yea can be used as a noun and also as an adverb. As an adverb it simply means yes, whereas as a noun, it refers to an affirmative answer. It is also used in another sense, whereby it lays emphasis on a more appropriate word than the one previously used in a sentence.

Yeah is a more informal way of saying yes. It can be very well substituted with yep, yup, or even yea for that matter. It's sometimes also used to mean 'whatever'.
Yay is an exclamation, and is therefore used with an exclamation mark (Yay!). It is mostly used to express excitement, encouragement, or exhilaration. However, in some cases it is also used to mean, 'to this extent' or 'to a considerable degree'.
Yea sounds more like may or lay. It shouldn't be pronounced as ya or yia, confusing it with the pronunciation of yeah.

Yeah can be pronounced as yah+uh. The sound of the concluding 'h' should be audible.

Yay is pronounced as hey or lay, with more emphasis on 'a'.
Although the rule seemed logical, majority voted nay, and a mere 4 people voted yea.

After listening to the tempting job offer, she couldn't resist to say yea.

A few yeas were very critical for the ruling party to win.

The burger was filled, yea, stuffed with cheese.
Yeah dad, I'll do it when I find time.

Yeah, so, what's the big deal?

Oh yeah, I think I kept my suitcase on the loft.

Yay! It's finally Christmas.

In the past, the cakes made by this bakery were yay big.

We rocked the performance. Yay! But the judges seem to be partial. Boo.
Yea and yeah are just casual ways of saying yes, if your affirmation is a special one (like replying to a guy who proposed you), you could be a little naughty and say yes in a different languages. Finally, don't forget to use these three words in the right context.