Two or more words with very closely related meanings are called synonyms. They can often, though not always, be substituted for each other in sentences. In the appropriate circumstances, we can say, What was his answer? or What was his reply? with much the same meaning. Other common examples of synonyms are the pairs: almost/nearly, big/large, broad/wide, buy/purchase, cab/taxi, car/automobile, couch/sofa, freedom/ liberty.

We should keep in mind that the idea of “sameness” of meaning used in discussing synonymy is not necessarily “total sameness.” There are many occasions when one word is appropriate in a sentence, but its synonym would be odd. For example, whereas the word answer fits in the sentence Sandy had only one answer correct on the test, the word reply would sound odd. Synonymous forms may also differ in terms of formal versus informal uses. The sentence My father purchased a large automobile has virtually the same meaning as My dad bought a big car, with four synonymous replacements, but the second version sounds much more casual or informal than the first.