el·dest 
/ˈɛldəst/ adjective
always used before a noun /ˈɛldəst/ adjective : of the greatest age : oldest ◊Eldest is usually used to describe people who are members of the same family.
▪ my eldest brother/sister/son/daughter/child
▪ my eldest brother/sister/son/daughter/child
the eldest
— used in comparing the ages of people who are members of the same family ▪ He's the eldest of her three brothers.
