The word "another" is used to refer to an additional thing or person that is different from the one or ones already mentioned. It implies the existence of something else that is similar or can be used in place of the first.
The word "another" originates from the combination of "an" (meaning "one") and "other," which comes from Old English "ōðer," meaning "other" or "another." The current form has been influenced by Middle English.