Phrynichus Arabius (//; Greek: Φρύνιχος ὁ Ἀράβιος) or Phrynichus of Bithynia (Greek: Φρύνιχος ὁ Βιθυνός) was a Greek grammarian who flourished in 2nd century Bithynia, writing works on proper Attic usage. His name is also transliterated as Phrynichos or Phrynikhos.
The Suda states:
- Φρύνιχος, Βιθυνός, σοφιστής. Ἀττικιστὴν ὑπ' Ἀττικῶν ὀνομάτων βιβλία β#, Τιθεμένων συναγωγήν, Σοφιστικῆς παρασκευῆς βιβλία μζ#, οἱ δὲ οδ#. 
- "Phrynichus of Bithynia, sophist. He wrote
- Atticist, or On Attic Words (Ἀττικῶν ὀνομάτων) in two books;
- Collection of Usages (Τιθεμένων συναγωγήν)
- Sophistic Preparations (Σοφιστικῆς παρασκευῆς (47 books, but some say 74)
As models of Attic style Phrynichus assigns the highest place to Plato, Demosthenes, and Aeschines the Socratic. The work was learned, but prolix and garrulous. A fragment contained in a Paris MS. was published by B. de Montfaucon, and by I. Bekker. Another work of Phrynichus, not mentioned by Photius, but perhaps identical with the Atticist mentioned by Suidas, the Selection (Ἐκλογὴ) of Attic Words and Phrases, is extant. It is dedicated to Cornelianus, a man of literary tastes, and one of the imperial secretaries, who had invited the author to undertake the work; it is a collection of current words and forms which deviated from the Old Attic standard, the true Attic equivalents being given side by side. The work is thus a prescriptive and reforming lexicon antibarbarum, and is interesting as illustrating the changes through which the Greek language had passed between the 4th century B.C. and the 2nd century A.D.
Editions of the Eklogê, with valuable notes, have been published by C. A. Lobeck (1820) and W. G. Rutherford (1881); Lobeck devotes his attention chiefly to the later, Rutherford to the earlier usages noticed by Phrynichus. See also J. Brenous, De Phrynicho Atticista (1895).
- I. Avotins "The sophist Aristocles and the grammarian Phrynichus", Parola del Passato 33 (1978), 181–91
- J. de Borries Phrynichi Sophistae Praeparatio Sophistica (Leipzig 1911)
- E. Fischer Die Ekloge des Phrynichos (SGLG 1, Berlin 1974)
- This article incorporates text from a publication now in the public domain: Chisholm, Hugh, ed. (1911). "Phrynichus". Encyclopædia Britannica. 21 (11th ed.). Cambridge University Press.
- Phrynichi eclogae nominum et verborum atticorum, Chr. Augus. Lobeck (ed.), Lipsiae, in libraria weidmannia, 1820.
- The new Phrynichus, being a revides text of The Ecloga of the grammarian Phrynichus, W. Gunion Rutherford (ed.), London, Macmilla and Co., 1881.