Abbott-Smith Manual Greek Lexicon
Ἀββά (G5)
3 Ἀββά (T, -ᾶ ), indecl. (Aram, אַבָּא , emphatic form of אַב = Heb. אָב , father ), used in the phrase Ἀ. ὁ πατήρ , Abba, Father (v. Swete on Mk 14:36 ): Mk 14:36 , Ro 8:15 , Ga 4:6 .†
G. Abbott-Smith, A Manual Greek Lexicon of the New Testament (1922) — public domain