Leave it to Ma Bell. When no word exists, she invents one. That's apparently why and how the symbol # is called an "octothorpe."

When I reported a few days ago that two researchers and I had been going out of our collective minds trying to find out what you call a #, it never occurred to me that the answer lay in the lower right-hand corner of the keyboard of a touch-tone phone.

The # symbol is found on all touch-tones, of course. According to Bell System literature, it has been called an "octothorpe" ever since touch-tones were introduced about 15 years ago. Several readers mailed in pages torn from computer manuals and service booklets as proof.

But Ma Bell is silent as to why "octothorpe" was chosen, where it came from and what name the symbol might have had before 1967. Nor does Ma explain why a prefix meaning "eight" was chosen rather than a prefix meaning "nine." After all, there may be eight "points" in an octothorpe, but any tic-tac-toe addict knows that there are nine squares.

Equally silent are the eight dictionaries I checked. None lists "octothorpe." None even lists "thorpe."

Still, "octothorpe" is as close as we've gotten to an accepted answer -- as unsatisfying and unofficial as it may seem. Many thanks to John D. Fogarty of Columbia, Bruce Boston of Fairfax, Chuck Pinkham of Gambrills, Md., Amy Weinstein of Northwest, Milly Edwards of Fairfax, Bill Werner of Sterling, Eric Hughes of Annandale, Ken Zemrowski of Arlington, Gerre Jones of Northwest and Don Bailey of Bethesda--octothorpers all.

We can't close the subject of #, however, without mentioning several other submissions -- some of them serious, some of them fanciful.

Susan Crosby of Berwyn Heights, who works for the Congressional Research Service of the Library of Congress, reports that Webster's New Collegiate Dictionary (1973) calls # a "delimeter." I let my fingers do some walking, and Susan is right.

However, the 1973 New Collegiate doesn't explain or expand. And "delimeter" doesn't even appear in seven other dictionaries. So, while Susan is the only contestant who has provided a dictionary citation, her "delimeter" seems to have raised more questions than it answered.

Ditto David DeBerry of Southeast. A travel agent, Dave says that he once took a computer training course from American Airlines, which called # a "cross of Lorraine." Presumably, the reference is to heraldic armor used at one time in the Alsace-Lorraine region of France. But again, I could find no clear proof in several histories, and several more encyclopedias.

Proofreaders and editors (among them David Reynolds of Alexandria and Art Brigham of Silver Spring) noted that # is a printer's mark meaning "insert more space here." Ted Vincenty of Washington Grove and Georgina Bohn of Reston add that they call # a "double cross," for no particular reason.

And who says computer people are unimaginative? Joseph B. Creegan Jr., a manager at the Rosslyn offices of Ketron Inc., says his troops call # a "crunch."

"The symbol # plays an important part in computer programming language that we use daily to build and analyze mathematical models," Joe writes. "Anything that is used regularly becomes part of the everyday vocabulary and must have a pronounceable, understandable name." Therefore, "crunch."

"The derivation of 'crunch' goes as follows: Most of us recognize # as the pound sign. Well, what happens when you pound on something? You crunch it, of course."

Science marches on.