The new frontier of expanding vocabulary.

• Position: YOUR LIFE

You are reading an article, book, or newspaper and come across a word that you do not recognize. "It's something [that happens] all the time," says William Rapaport, associate professor of computer science at the University at Buffalo (N.Y.). "You come across a word you don't know; you decide if you want to understand the passage; you need to understand what the word means, but it's either not in the dictionary or you are too lazy to look it up. Or you ... look it up and you can't understand the meaning from the dictionary ... and there's nobody around to ask."

Rapaport and colleague Michael Kibby, professor of learning and instruction in the Graduate School of Education, have spent years researching a concept called contextual vocabulary acquisition, or CVA, which readers can employ to figure out meanings of unfamiliar terms.

CVA--using clues in the text surrounding an unknown word to discover its meaning--is "not a once-in-a-while thing," but a commonly practiced technique, Rapaport maintains. "Most of our vocabulary--around 90%--is acquired this way. People know the meanings of more words than they are explicitly taught, so they must have learned most of them as a by-product of reading or listening."

Socioeconomic class, however, has "a huge impact" on how many words a person will learn, Kibby points out. Studies show young children of professional parents hear an average of 47,000 words, as...