Other forms: elders
Elder means older than the other one, especially between two people in a family. The elder brother, the elder sister.
It is restricted in a way that older is not, since it goes only before a noun and only about people, so nobody says an elder building. Eldest is the superlative for three or more. The noun means a respected older member of a community, and elders are a real institution in many cultures. There is an unrelated tree called an elder, whose flowers make cordial.
Proto-Indo-European
*h₂el- (grow)
Proto-Germanic
*alþizô
Old English
eldra
Middle English
eldre
English, today
elder
From Middle English eldre, from Old English eldra, yldra, ieldra, from Proto-Germanic alþizô. The vowel change from a to e triggered by the following i is called umlaut or I-mutation.
Etymology from Wiktionary, CC BY-SA