βῦ
From LSJ
διὸ καὶ μεταλάττουσι τὴν φυσικὴν χρῆσιν εἰς τὴν παρὰ φύσιν αἱ δοκοῦσαι παρθένοι τῶν εἰδώλων → therefore those professing to be virgins of the idols even change the natural use into the unnatural (Origen, commentary on Romans 1:26)
English (LSJ)
exclamation of admiration, EM216.55.
Spanish (DGE)
buh exclamation de asombro EM 216.55G.