eldest

1. superlativesuperlative form of old: most old; greatest in age or seniority.

   The eldest son was usually given the name of his paternal grandfather, later children those of other relatives.

   1945, E[lizabeth] G[idley] Withycombe, “Introduction”, in The Oxford Dictionary of English Christian Names, Oxford, Oxfordshire: Clarendon Press, →OCLC, page xiii

2. card games(of a player) Receiving cards from the dealer first, before any other players.
3. card games(of a hand) Having higher, or superior cards.

   Each player draws a card, and the lowest becomes eldest hand.

   2003, The Card Game Set, Thunder Bay Press

plural eldests

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