LSJ
ατος, τό, that which is given in advance, prepayment, advance of money, PCair. Zen. 269 (iii BC), Plb. 29.8.8, 15.25.16 (pl.), JHS 11.122 (Ceramus), PTeb. 42.15 (ii BC), Hdn. Gr. 2.935, Hsch. s.v. ἀρραβών.
Liddell-Scott-Jones, Greek-English Lexicon (9th ed., 1940)
Pape
τό, das Vorhergegebene, Hesych. v. ἀρραβών.
Pape, Griechisch-deutsches Handwörterbuch (3. Aufl., 1914)