About 40% of English words are polysemous. This means that they have more than one meaning. Some words, such as run or set have more than thirty different meanings. Polysemous words can cause difficulty in contexts where the meaning is other than the primary* meaning of the word.
*In this case, primary refers to the sense of the word that the student has learned frst. For example, ESL students generally first learn the word table as referring to an item of furniture. So they might be confused when the mathematics teacher tells them to put their data in a table. Indeed, mathematics is full of words that ESL students are likely to have learned first with their everyday meaning: mean, power, even, volume, root, etc.
Here are a few examples of polysemous words. They are shown first in a primary-meaning context and followed by secondary-meaning context.
Mason (1978) investigates the effects of polysemous words on sentence comprehension in a research study of the same name. The study supports the intuitive assumption of ESL teachers that texts with polysemous words used in their non-primary sense are more difficult to process than texts with primary-sense polysemous words. Here is the concluding sentence of the abstract:
It is apparent that the presence of polysemous words in text materials is one source of comprehension difficulty. (Source, .pdf)
It is important that teachers are aware of the polysemic nature of much English vocabulary, and the problems that this can cause non-native speakers. It is helpful if teachers can alert ESL students to words with a different meaning than the one that the students will likely have learned first. These can be words that the teachers themselves use in speaking or writing, or words that students encounter in their textbooks and other prescribed reading texts.