Aelius Dionysius was a Greek grammarian and lexicographer from Halicarnassus. He was active during the reign of the Roman emperor Hadrian in the 2nd century CE. His Roman family name suggests he or his family held Roman citizenship, indicating integration into the imperial system. He worked during the period known as the Second Sophistic, a time of renewed interest in classical Greek language and culture.

His professional role was that of a grammarian, and he was part of the Atticist movement. This movement sought to define and preserve the classical Athenian Greek of the 5th and 4th centuries BCE as the standard for educated writing and speech.

His known work is a lexicon titled Attic Words. The book itself has not survived, but it is quoted extensively by later Byzantine scholars and compilers. These quotations are how modern knowledge of his work is preserved.

According to modern scholars, his primary significance lies in his contribution to the Atticist tradition. His lexicon was a major source for later influential dictionaries, such as the Etymologicum Magnum and the lexicon of Hesychius of Alexandria. Through these works, his efforts helped transmit knowledge of classical Greek vocabulary. He is seen as part of the scholarly wing of the Second Sophistic, which aimed to regulate language use for the elite of the Roman Empire. The citations of his lost work remain crucial for understanding the linguistic debates of his era.