I have noticed that in Northern Virginia the little tributaries of the Potomac are called "runs." There's Four Mile Run, Cameron Run, Dead Run, Spout Run, to name a few. In Maryland, these seem to be called "creeks" or "branches," i.e., Paint Branch, Northwest Branch, Sligo Creek, Rock Creek, etc. Is there a difference between a branch and a run?

Brigid G. Nuta, Montgomery Village

No. A creek is a branch is a run. They're pretty much synonymous, and all mean a small stream.

While Virginia might seem especially "runny," there are runs in Maryland, just as there are branches in Virginia, said Roger Payne, head of the U.S. Geological Survey's geographic names program.

"The reality is that 'run' is used extensively on both sides of the Potomac," he said, "in Maryland as well as Virginia, not to mention heavily throughout Pennsylvania and the northeastern part of West Virginia."

It's also found in Ohio, said Joan Hall, chief editor of the Dictionary of American Regional English, a cool reference book that shows where you're likely to hear various words describing different things. Nomenclature is usually a legacy of what sort of people settled a certain area, said Joan. In New York state, you'll encounter the word "kill" for a stream or creek, a remnant of the early Dutch settlement in that area. ("Kill" is the Dutch word for "stream.")

Our area was settled mostly by the English, and Roger Payne thinks this is what happened: Back home in England, the term "creek" was used to refer to streams that were influenced by the tides. Since this applied to the first streams settlers encountered here in the 17th century, they named them as such.

But as they began to move inland, said Roger, "very quickly they encountered these very fast-flowing streams, and they just didn't know what to call them. They didn't have a word. And hence the generic 'run.' "

What's a bit of a mystery is why "run" never caught on elsewhere in the country. "Branch" is common nationwide, typically to describe a stream that splits off another tributary. ("Fork" and "prong" are other words sometimes encountered; they might have had distinct meanings that are now lost, said Roger.) "Brook" was originally confined to New England, but now it's all over the Northeast.

The federal government has no official position on what is a creek or a branch or a run. It's all based on the perception of the people who named the various features.

"Generally speaking, I think everyone would agree that creeks are smaller than rivers and creeks flow into rivers," Roger said. "Having said that, a notable exception comes to mind: Here in Northern Virginia, near our offices in Reston, Little River flows into Goose Creek."

There is an exit on George Washington Parkway just before National Airport named "Roach's Run." Please tell me that the name doesn't mean what I think it means. Maybe it is named after a famous person named Jonathan Q. Roach who used to run there.

Jacob Fritz, Baileys Crossroads

A few months ago, I wrote a column about the facility that performs the official pollen count for the Washington area. It's at Walter Reed's Forest Glen Annex and is called the U.S. Army's Centralized Allergen Extract Laboratory.

I didn't have room to mention the thousands of allergy shots the lab prepares for members of the armed forces. One room is filled with refrigerated cabinets containing glass ampuls, each one filed according to the allergy it treats. There's cat, hamster, gerbil, rabbit. There's beans (string, kidney and pinto). There's tapioca and mackerel. One bottle held a brownish-yellow liquid. It was labeled "cockroach."

Of course, the way they make these allergy shots is to take a small amount of the offending agent, crush it up and put it in a sterile solution. Then that gets injected into the allergy sufferer. Which means people allergic to cockroaches get a little bit of ground-up cockroach. Paging Gregor Samsa! Gregor Samsa, please pick up white courtesy phone!

But this has nothing to do with the question. Roach's Run is not named for the annoying insect. The stream -- and thus the nearby bird sanctuary -- is named for the family of James Roach. He ran a brickworks near the stream and in 1841 built a mansion, called Prospect Hill, at what is now roughly 1230 S. Arlington Ridge Rd. Union troops made a mess of things there during the Civil War -- cut down trees, killed farm animals -- and the house was torn down in 1965 to make way for apartments.

And now to take things full circle: The original name of Roach's Run was Mill Branch.

'Run' to Camp!

Ah, nature. That's the idea behind Camp Moss Hollow. I didn't encounter any branches, creeks or runs while I was there, but there is a small pond for canoeing on and a pool for swimming in. Here's how to make a tax-deductible contribution so local at-risk kids can experience that and more:

Make a check or money order payable to "Send a Kid to Camp" and mail it to Family and Child Services, P.O. Box 96237, Washington, D.C. 20090-6237. To contribute online, go to www.washingtonpost.com/johnkelly. Click on the icon that says, "Make a Donation."

To donate by MasterCard or Visa by phone, call 202-334-5100 and follow the instructions on our taped message.

Julia Feldmeier helped research this column. Write: answerman@washpost.com.