From Middle Frenchpedant, pedante, from Italianpedante (“a teacher, schoolmaster, pedant”), of uncertain origin, traced by some sources to Latin paedagogans, present participle of paedagogare ( = to teach, from Greek "paedagogein" = to instruct children ). Confer French pedant.
The easiest way to define this word is someone who nitpicks the smallest of errors. For example, some think that those who are pedantic are looking down their noses at bad grammar usage. However, as one who really struggles to NOT correct people, I can say that, personally, it's because I truly want a person to know how to use a word correctly.
As an illustration, an educated man can use the word "went" instead of "gone", which is very common here in the deep south. Immediately, his education flies out the window, and his IQ drops at least 10 points to the person who notices the gaffe. If I used a word incorrectly like that, I would want to be corrected, in private, so I could make better use of the language in expressing myself in the future.
I guess to one who is a pedant, being pedantic is a compliment. haha!