-noun, plural -bodies.
a person who pries into or meddles in the affairs of others.
I, for one, have misused this word my entire life primarily because I never bothered to look it up and my internal definition of the word seemed to gel with everyone else's. I think the reason why this word is so often misused is because the actual meaning is very different from the combination of the two words that make it up. "Busy" has seven different definitions, the most often cited being "full of or characterized by activity" while "body" is obviously most often referring to the "physical person of an individual" hence the literal definition implied by the connecting of these two words would be that a busybody is one who is unable to refrain from physical activity. That is how I have always understood the word.
But apparently I'm incorrect. It seems that the real definition of busybody utilizes a far rarer definition for the first root word: "busy: officious; meddlesome; prying". This understanding of the word "busy" combined with "body" then takes on a different character, one far more suited to the actual definition.