An opaque engineering word list: Which words should a teacher focus on?

Word lists have become influential in the last twenty years, but do not help teachers identify which words to explicitly focus on in the classroom. In this paper, I argue that words chosen for an explicit classroom focus should be words that students are likely to have problems dealing with autonomously, and that these are polysemous words where the meaning required is not the usual meaning; in other words, opaque words. The paper shows how to create a list of opaque words for teaching engineering English at a Thai university by comparing the meanings of words in the context against the main meanings given in the online dictionaries that students often rely on. The resulting list shows that most opaque words are high-frequency words with unusual meanings.