"Beautiful and attractive," "honest and honorable," and "lazy and idle" are several examples of synonym pairs. Synonym pairs, which are two words that mean roughly the same thing, can be composed of words from any of the eight parts of speech as long as the two words are from the same part of speech.
Synonym pairs have two basic types of interaction: complete interchangeability and contextual interchangeability. Complete interchangeability is when a pair of synonyms mean almost exactly the same thing and can be used in place of each other in any context. Contextual interchangeability is when a pair of synonyms mean the same thing in one usage but not necessarily in another. For example, the words "expired" and "died" are synonymous when they are used in reference to the death of a person, but not when they are used in reference to the expiration of a passport.
While synonyms can be used in pairs, they are not exclusive; a single word can have multiple synonyms. Because of this, one cannot assume that two words that share a synonym are necessarily synonymous. For example, "fourth-year college student" and "elder" are both synonymous with "senior," but are not synonymous with each other.