A heteronym pair is a pair of words with a very specific connection and relationship. A pair of words that constitutes a pair of heteronyms will be identically spelled, but have different meanings, and be pronounced differently. In some rare cases, this type of group may include three different words, but heteronyms are usually found in pairs, at least in English and related languages. In terms of linguistic terminology, some refer to heteronyms as homographs that are not homonyms. Homographs are words that are spelled the same, and homonyms are words that are pronounced the same; heteronyms are examples of the former, but not of the latter.
Some types of heteronyms consists of a word that functions as both a noun and a verb, each with the same spelling. When this happens, different syllable stresses often identify either the noun or the verb for. For example, an English speaker might use the word “desert” as a verb, stressing the second syllable, or as a noun, stressing the first syllable. Because difference in stresses or phonetics apply to heteronyms, this is a prime example of this word pair.
Other similar sets of heteronyms are good examples for English language learners. In many of these longer words, with a suffix “ate”, the vowel sound at the end differs according to whether the word is a verb or adjective. One excellent example is the word “elaborate,” which as a verb means to expound on an issue or topic, and receives a long "a" sound in the last syllable. As an adjective, the word “elaborate” means grand or fancy, and does not receive a strong ‘a’ sound on the last syllable. As these words are spelled the same, but do not sound the same, they constitute a heteronym pair.
In other types of heteronyms, the double words do not have the same strong semantic connections. In other words, they don’t have similar root meanings, but simply represent coincidences where the finite combinations of letters in an alphabet lead to to identically spelled words that have nothing to do with each other. For example, the word “number” as a frequently used basic reference to enumerating items, contains a "b" sound, where the heteronym “number,” as a comparative form of the adjective “numb,” has a silent "b."
The rate of heteronym occurrence in a language has a lot to do with how that language is set up. For instance, in a tonal language where pronunciation varies a lot more than alphabetic spelling, the occurrence of these pairs of words will be common. In other languages with more extensive alphabets, this phenomenon may be less common.