This modest little word derives from the Old French naperon, meaning small table cloth. When it first made its way into the English language in the 1400s, it became Anglicised - quite reasonably - as napron. And so it stayed for 150 years or so, before becoming apron.
So where did the n disappear to? I hear you ask.
It didn't. Well, not exactly. It simply shifted to the left, as you can hear when someone talks about wearing an apron.
This phenomenon is called false splitting, and it's occurred more than once. For example, a ninkling became an inkling, a nauger became an auger, and that most English of snakes transformed from a nadder to an adder (thank heavens: Blacknadder just doesn't sound the same, does it?).
Mediaeval scribes didn't help. They wrote words so close together that it was often hard to tell where one ended and a new one started. Only an itwit would do that today.
The process can also work in reverse, with n being added to words that didn't originally have one. If you have a nickname, there was a time when what you had was an eke name (eke means additional - hence "eke out a living"). That little amphibious beastie called a newt was originally an eute.
Even proper names aren't exempt. Ned and Nellie are both thought to have emerged from the fond phrase "mine [insert object of affection's name here]". This led to "mine Ed" becoming misheard as "my Ned" and likewise with Ellie to Nellie.
But who would call someone "mine x" in the first place? Someone from before the 13th century is who. Until then, people didn't say my anything - it was always mine (mine wife, mine hovel, etc). When my became popular, mine was still reserved for use in front of words beginning with a vowel - just as we use an versus a today. But listeners began hearing it as my. If they hadn't, today we'd be lauding the Australian folk hero, Ed Kelly, and Eskimo Elle would be the one celebrated in that famous (and largely unprintable) epic poem.