Say it ain't so.

We've struggled for so long to resist that ugly little negative contraction, and now Merriam-Webster says "ain't" ain't so bad after all.

"Ain't" and 10,000 other new entries have made it into the newest edition of Merriam-Webster's Collegiate Dictionary. It's not the first dictionary to print the word, which has long appeared in unabridged dictionaries as well as Webster's New World Dictionary. But most identify it as substandard or slang. Merriam-Webster, the largest U.S. publisher of dictionaries, now includes it without any warning against its use.

Other words and terms that got the nod are signs of the times: safe sex, date rape, boom box, politically correct, megahit, downscale, wire fraud, voice mail, significant other, veg out.

You'd think Noah Webster, great granddaddy of American English, would be turning over in his grave.

But he ain't.

Webster was a renegade lexicographer who would likely rejoice in the new 10th edition of Merriam-Webster's Collegiate Dictionary, now in bookstores.

Friday, incidentally, is the 150th anniversary of his death.

"I'm sure part of his reaction to ain't would be defiant pride in its colloquial Americanism," said Frederick Mish, editor-in-chief of Merriam-Webster Inc. "He very much favored all sorts of words if they were widely used, not just the good words."

Not that ain't is really a bad word. Language experts say it has just gotten a bad rap.

"The sooner that ain't is accepted as standard American English, the better off we will be," said Ron Newman, director of English composition at the University of Miami. "It is a perfectly serviceable word, and from the purely linguistic point of view it is as defensible as don't and won't." Ain't has been around. According to Merriam-Webster's new dictionary, it goes back to 1778. It's defined as:

* am not; are not; is not;

* have not, has not;

* do not; does not; did not.

"Although widely disapproved as nonstandard and more common in the habitual speech of the less educated, ain't in senses 1 and 2 is flourishing in American English," the dictionary explains.