Aristonymus was an Athenian comic poet active in the late 5th and early 4th centuries BCE, during the period of Old Comedy. He was a contemporary of more famous playwrights like Aristophanes. According to a later Byzantine source, he was the son of the comic poet Xenarchus, though this relationship lacks earlier confirmation.

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 survive because later ancient scholars and lexicographers quoted lines from it to illustrate rare words or unusual expressions, indicating his work was noted for its distinctive language. The plot remains unknown.

Modern scholars regard 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 for offering glimpses into the linguistic style, topical humor, and competitive world of Athenian theater. While his historical influence is limited by the loss of his plays, the surviving pieces aid researchers in reconstructing aspects of daily life, religious satire, and the vocabulary of ancient Greek comedy.