eldest

/ˈɛldəst/

/ˈɛldɪst/

Someone who's described as eldest in their family was born first. Your eldest sister is the oldest one.

Use the adjective eldest when you're describing people in terms of birth order: the oldest is the eldest. Your eldest friend is older than your other friends. You can also use the word as a noun, meaning "firstborn." Your mom might introduce you by saying, "This is my eldest." It's a somewhat formal, old fashioned word, much less popular today than "oldest."

Definitions of eldest

1. adjective

   first in order of birth
   synonyms: firstborn

   first

   preceding all others in time or space or degree
2. noun

   the offspring who came first in the order of birth
   synonyms: firstborn

   type of:

   issue, offspring, progeny

   the immediate descendants of a person