What do you call those soft rolls of dust that collect on the floor under your bed? Many people know them as dust bunnies. But in parts of the Northeast, you'd call them dust kitties; in the South, house moss; in Pennsylvania, you might call them woolies.

There are, in fact, at least 174 names by which Americans call these bits of fluff, including bunny tails, frog hair, cussywop, woofinpoofs and—perhaps most evocatively—ghost manure.

That we can identify these words today is largely a testament to the vision of one man: Frederic Cassidy, a professor of English at the University of Wisconsin in Madison who conceived the Dictionary of American Regional English (known as DARE) in a 1962 speech to the American Dialect Society.

Mr. Cassidy died in 2000, at the age of 92, having made it to "O" in his quest to catalog American English in all its rip-staving (that is Ozarkian for rip-roaring) regional diversity. His tombstone bears a simple inscription: "On to Z!"

"That was his rallying cry for about the last decade of his life," said Joan Houston Hall, 65, who joined DARE in 1975 and took over as its chief editor after Mr. Cassidy's death. In March, Harvard University Press will publish the Dictionary's Volume V, finishing off the alphabet with slab through zydeco, nearly half a century after the first fieldworkers fanned out in "Word Wagons" to 1,002 communities across America, administering a 1,600-item questionnaire to sometimes-suspicious, often-perplexed locals.