Distinguish between Masculine and Feminine Nouns in French within 100 characters
CJam, 0 incorrect, 32 29 bytes

This code uses a few odd characters (some of them unprintable), but they are all well within extended ASCII range. So again, I'm counting each character as a single byte.

"un"'el2b"zPB:  ":i+:%2/*


Due to the unprintable characters, I'm sure Stack Exchange swallows some, so you might want to copy the code from the character counter (it shows bytes with UTF-8 encoding, which is suboptimal for this challenge; also, the link doesn't seem to work in Firefox, but does in Chrome).

Test it here.

After some more discussion in chat, we figured that the regex golfing wouldn't bring us much further. So following an earlier (joking) suggestion of mine we started looking into manipulating the character codes of the words with certain functions, such that all words from one group would yield a number with some property that is easy to check. And we got luckier than we expected! Here is what the code does to the words:


Implicitly convert the characters in the word to their code points.
Interpret those as digits in base 2 (yes, the digits will be much larger than 0 or 1, but CJam can handle that).
Repeatedly take the result modulo... the following numbers: [133, 122, 80, 66, 58, 26, 20, 14, 9, 4]. This sequence of numbers is itself encoded as the code points of a string (this is where the weird and unprintable characters come in).
As if by magic, all 25 masculine nouns yield 0 or 1, and all 25 feminine nouns yield 2 or 3 with this procedure. So if we divide this by 2 (integer division) we get zeroes for masculine nouns and ones for feminine nouns.


To round it off, we push "un" on the stack, the we push a single e. Then we read the input word from STDIN and perform the above computation, and finally multiply the e by the result.

I have never folded modulo onto any list before, and I feel like I never will again...

Many thanks for xnor and Sp3000 for throwing ideas around and helping with the search for divisor chain.