GET OUT THE PITH HELMETS; WE ARE ABOUT TO EMBARK ON a linguistic expedition to determine the origins of the word joanin'. The letters of protest poured in last week, with readers howling in outrage that we had dared to suggest in our May 10 column that the verb joan (meaning to insult) was possibly derived from Joan Rivers.

"I've been a college graduate for two years," says Cliff Thompson of Brooklyn, N.Y., "and I remember the word {jonin' to him} from my days at Richardson Elementary School. It was big in the black community when Joan Rivers was still waiting for her big break."

"The term joaning is over 20 years old," says Andrew Jackson of Suitland. "It was in common use around 1963-1967. I am 38 years old and graduated from Mackin High School in 1967."

"The term joaning was widely used among white blue-collar kids when I was a teen-ager in Prince George's County in the early 1960s," says Joseph A. Hines of Hyattsville.

"I am a woman of 70 years and I have heard that word, from the name Jones, as far back as my teens," says Evelyn P. Fagin of Washington.

"I regret to say that we must regard the attempt to find in jonin' a reference to Ms. Rivers' performance style as nothing more than a folk etymology -- an ingenious and plausible but historically inaccurate speculation," says Ira Gitlin of New Carrollton. And to prove his point he cites the book Black English by J.L. Dillard (Random House, 1972): "One of the more interesting {modes of discourse engaged in by inner-city black adolescent males} is called jonin' by the Washington community."

For further elucidation we called the expert himself. Dillard, the author of several books on black English and a professor at Northwestern State University in Natchitoches, La., said the word was popular in the Washington black community in the '60s. "Jonin' is a quasi-ritualized game of verbal insult, with recognized rules for excelling and status rewards," he said.

But where did it come from? "There was a theory at one time that it came from {the biblical} Jonah, but there's no basis for that," said Dillard. "For the record, I'd have to say that I really don't know where it came from. It may be one of those slang words that has a life of its own."

Whether it's jonin', or joanin', it apparently didn't start with Joan Rivers. And certainly not Joan Mondale. Spike Jones? Don't even think about Joan of Arc.

Next question? How to pronounce Natchitoches.