Aristonymus was an Athenian comic poet active in the late 5th and early 4th centuries BCE, during the period known as Old Comedy. He was a contemporary of more famous playwrights like Aristophanes. According to a later Byzantine encyclopedia, he was the son of another comic poet named Xenarchus, but this relationship is not confirmed by earlier evidence. An ancient inscription records that a comic poet named Aristonymus won a victory at the City Dionysia festival in Athens, which is generally believed to refer to him.

Only one of his comedies is known by title: The Priests. The play itself is lost, but fragments of its text survive because later ancient scholars and dictionary writers quoted lines from it. They used these quotations to explain rare words or unusual expressions, suggesting his work was notable for its distinctive language. The plot of the play is unknown.

Modern scholars view Aristonymus as a representative of the many comic poets from the vibrant era of Old Comedy whose works have not survived intact. His fragments are valuable because they offer glimpses into the linguistic style, topical humor, and competitive world of Athenian theater. While his historical influence is limited due to the loss of his plays, the surviving pieces help researchers reconstruct aspects of daily life, religious satire, and the vocabulary of ancient Greek comedy.