Finik

A household nickname ("Date/Finik") used within the Chekhov family circle for one of Anton's siblings, here paired with "Ma-Pa" and contrasted in the same sentence with "мать и батька" (his parents, "Mother and Father") -- confirming Finik denotes a sibling rather than a parent, though which sibling is not securely identifiable from the surviving letters. Distinct from the unrelated character "Bogemsky, otherwise known as Finik" nicknamed in.