LOS ANGELES — Los Angeles -- When actor Tony Randall first heard the word "campestral," he lunged for his favorite dictionary. The Felix Unger of words -- def. finnicky, persnickety, discriminating -- Mr. Randall loves expanding his vocabulary. So much so that publisher Houghton Mifflin selected Mr. Randall to sit on the usage panel of its American Heritage Dictionary. The third edition was just published. "I'm a dictionary reader," Mr. Randall, a New York resident, said during a recent phone interview. "I always have been." Campestral, by the way, means relating to open fields. And lexicography -- the act, process, art or work of writing or compiling a dictionary or dictionaries -- is big business for the four major publishing houses. Their target audience is students, particularly college students, who are presently packing their bags and books and heading back to school. With an explosion of dictionaries on the market, selecting the one that best suits a student's needs can be difficult, experts say. Steven Parker, a political science major at California State University, Northridge (CSUN), keeps two dictionaries -- a Webster's and an American Heritage -- at home to help him hunt for unfamiliar terms bandied about by professors. "I like expanding my vocabulary," the 22-year-old Van Nuys resident said. "If something catches my eye, I'll take a minute to look at it or words surrounding it." Many people become attached to a dictionary and will keep it for years, even after newer ones are published. "There is a rule in lexicography, the moment a dictionary is published it is obsolete because the language has continued to change," said Louis Milic, a Cleveland State University professor and secretary-treasurer of the Dictionary Society of North America. "The soundest principle for a word person is, the latest dictionary is the best," he said. But the choice can be confusing for the person looking to buy a general-purpose dictionary. It's not a simple matter of just getting "the Webster." You've got your Random House Webster's College Dictionary. Then there's Webster's Ninth New Collegiate Dictionary. And the Webster's New World Dictionary. And there are a host of dictionaries that use the name Webster, which is in the public domain, that are unrelated. So forget the name and look to reputable publishers, said Kenneth Kister, author of Kister's Best Dictionaries for Adults & Young People (Oryx; $39.50). The four main publishers of college-level dictionaries in the United States are Houghton Mifflin Co., Random House, Merriam-Webster and Prentice Hall, a division of Simon & Schuster. If you just need one to quickly check spelling and basic definitions, a small dictionary of 50,000 terms may be all you need, Mr. Kister said. "But if you are a writer, teacher or serious student and using words in a more serious manner, you need a larger dictionary," he said. The 20-volume Oxford English Dictionary, also known as the OED, is considered the Cadillac of dictionaries. At more than $2,000 for the set, it is the most expensive. "One word will cover pages," Mr. Kister said. The OED is the dictionary of choice when CSUN librarians are called upon to answer reference questions, said Wayne Cohen, reference processing supervisor. But other smaller dictionaries are scattered throughout the library. "They're everywhere," he said. "They have to be handy for students. We have them on every floor on these podiums. They are just a tool a student has to have." The most popular college-level dictionaries contain 150,000 to 180,000 entries and cost about $20. Dictionary buyers might want to consider whether they want a lot of guidance from a dictionary. Descriptive dictionaries tell how language is used. Many older dictionaries are known as prescriptive and tell us how language ought to be used. "Most lexicographers are on the side of descriptives," Mr. Kister said. "Our job is to tell how language is used." Dictionary buyers also might want to consider how readable the dictionary is, whether it contains confusing symbols and abbreviations. "If you're somewhat intimidated by a dictionary as some people are, look for a dictionary that is user friendly," Mr. Kister said. "The only way you can do this is go to a bookstore or library, get the major dictionaries out, and sit down and compare them." Look up the same word in each dictionary and compare the definitions, he suggested. "If you take a better dictionary and run the same kind of little test against a dictionary in the supermarket, you'll be shocked," Mr. Kister said. "Usually those dictionaries in the supermarket are junk." The dictionary can become almost like a best friend, experts say. "Here's the best suggestion: Spend a lot of time with it," Mr. Milic said. "It contains so much more information than any person has. It's worth reading in bed every night. It is the literate person's bible."