oldest

adj

1. (form-of, superlative)superlative form of old: most old

   “An interesting feature of the church is the invisible clock, which you can hear thumping away as you enter. Constructed in 1525, it is one of the oldest timepieces in England. It chimes the hours and the quarters, and every three hours it plays a hymn. But it has no faces.”

noun

1. The oldest child in a family, or individual in a group.

   “My oldest always forgets to turn the living room lights off before bed.”