Ammonius Grammaticus is the supposed author of a treatise titled Peri homoíōn kai diaphórōn léxeōn (περὶ ὁμοίων καὶ διαφόρων λέξεων, On the Differences of Synonymous Expressions), of whom nothing is known.

He was formerly identified with an Egypt

Egypt

Egypt , officially the Arab Republic of Egypt, Arabic: , is a country mainly in North Africa, with the Sinai Peninsula forming a land bridge in Southwest Asia. Egypt is thus a transcontinental country, and a major power in Africa, the Mediterranean Basin, the Middle East and the Muslim world...

ian priest who, after the destruction of the pagan temple at Alexandria (389), fled to Constantinople

Constantinople

Constantinople was the capital of the Roman, Eastern Roman, Byzantine, Latin, and Ottoman Empires. Throughout most of the Middle Ages, Constantinople was Europe's largest and wealthiest city.-Names:...

, where he became the tutor of the ecclesiastical historian Socrates

Socrates Scholasticus

Socrates of Constantinople, also known as Socrates Scholasticus, not to be confused with the Greek philosopher Socrates, was a Greek Christian church historian, a contemporary of Sozomen and Theodoret, who used his work; he was born at Constantinople c. 380: the date of his death is unknown...

. But it seems more probable
that the real author was Herennius Philo of Byblus, who was born during the reign of Nero

Nero

Nero , was Roman Emperor from 54 to 68, and the last in the Julio-Claudian dynasty. Nero was adopted by his great-uncle Claudius to become his heir and successor, and succeeded to the throne in 54 following Claudius' death....

 and lived till the reign of Hadrian

Hadrian

Hadrian , was Roman Emperor from 117 to 138. He is best known for building Hadrian's Wall, which marked the northern limit of Roman Britain. In Rome, he re-built the Pantheon and constructed the Temple of Venus and Roma. In addition to being emperor, Hadrian was a humanist and was philhellene in...

, and that the treatise in its present form is a revision prepared by a later Byzantine editor, whose name may have been Ammonius.