All these years, a number of fans have assumed that it's pronounced "N-E-S," with each letter spoken individually, while others have called it simply "NES." Turns out the latter group was right all along.
The correct pronunciation was uncovered in the recently released 3DS game WarioWare Gold. The game has a virtual museum showcasing various pieces of Nintendo history. Some Twitter users, including gamer Kyle McLain, have pointed out that the Japanese version of the game features a slide that shows the NES, and that the accompanying description provides the correct way of saying the console's name.
Eurogamer even asked one of its resident Japanese speakers to confirm the description text to ensure the accuracy of the pronunciation. They said that the correct pronunciation of the console is indeed "Ness."
How To Pronounce NES
That certainly makes a lot of sense, as saying N-E-S is quite a mouthful. Ness sounds simple, clean, and quick, and it's also a lot less awkward than saying "Nez." Nintendo purists will probably refrain from saying the acronymized version, though, and opt instead to pronounce the entire thing: Nintendo Entertainment System. However, when brevity is of utmost importance, saying Ness would be fine — and most importantly — correct.
Nintendo might have given a clue to the console's proper pronunciation years ago, actually. Many people have long speculated that Earthbound character Ness is a callback to the retro machine, which certainly makes sense. It's very typical of Nintendo to hide Easter eggs within its own games, and it wouldn't be a surprise if Ness is indeed some form of reference to the NES.
Again, however, not everyone is welcoming Nintendo's official pronunciation, just like when people disagreed with the actual creator of GIF on the image file's pronunciation. The creator says it as "Jiff," but others prefer "Gif" as in "gift" without the T, or "G-I-F," with each letter pronounced.
WarioWare Gold, the game that contains the NES reference, was released for the 3DS just days ago, serving as one of the last remaining titles to roll out as the console nears the end of its lifespan. Similar to previous WarioWare titles, it's a collection of minigames that speed up the longer it's played. WarioWare Gold is perhaps what one would say the ultimate mashup title, as it incorporates various input methods — blowing on the mic, tilting the system, and more — featured in past iterations of the game.