Abbott-Smith Manual Greek Lexicon
ῥακά (G4469)
1 * ῥακά (T, ῥαχά ), usually taken to represent the Aram. רֵיקָא , a shortened form of רֵיקָן , "empty," as vocalized in the Galilæan dialect; an expression of contempt, raca : Mt 5:22 (cf. DB , iv, 191 f.; and for other explanations, v. Zorell, s.v.).†
G. Abbott-Smith, A Manual Greek Lexicon of the New Testament (1922) — public domain