The word "only" is an adverb that indicates exclusivity or limitation. It is used to specify that something is singular or unique, often emphasizing that no other options or alternatives exist. For example, saying "I only have one apple" means there are no other apples available. In addition to its use in everyday language, "only" can also function as an adjective. In this context, it describes something that is the sole example of its kind. For instance, "She is the only student in the class" highlights that she is the unique individual among her peers.