• Is a crossword puzzle clue a definition of a word? • Can you enter to exit? • Are unrecoverable errors recoverable? • How can a word like “caution” mean “guarantee”? • What is it that happens unless you do something else? . . . This chapter is about the ways in which elements of language are at times able to correspond to each other in usage and in meaning. It explains equivalence, the baseline for distinctions between words, and clarifies widespread misconceptions about synonyms. It shows that words have values that are sometimes obvious and sometimes concealed. These concepts are relevant to all word choices in language, and they must be considered with due attention with translation of a user interface or documentation into another language. Ambiguity and culture are the two big issues that will inevitably come to the fore at such a time. It will also become clear that there are gaps to be filled in languages, and that interference and confusion are bound to get in the way. Multiple language environments create their own special demands with respect to all of these concepts. In a typical crossword puzzle, we are asked to think of words that correspond to descriptions or suggestions of their meaning. Because a crossword is a kind of game, the clues may well be phrased so as to make the word discovery difficult. By contrast, in dictionaries, descriptions of meaning are meant to correspond much more directly to designated words. A direct link is made between a particular language element—a word or phrase—and the language used to express its meaning, which stands in or substitutes for that element in a variety of ways. Definition is one way, within one language; translation is another way, between languages. Equivalence, in the sense of a perfect match on the level of meaning, may be achieved through definition, which draws on a rich range of language resources, but equivalence is much more problematic in translation. In translation into a target language, a word with exactly the same meaning may not exist.