Aorist passive, third person plural, of the verb βδελύσσω (cf. beta 205, beta 206). Evidently quoted from somewhere; perhaps Psalm 13.1 LXX or Psalm 52.2 LXX.
In Attic this verb (in the form βδελύττομαι ) is used only in the middle, with the aorist passive, meaning "I feel disgusted, I feel sick" (e.g. Aristophanes, Wasps 792). Later, for example in the LXX, the active is used causatively and the aorist passive has a passive sense, as in this entry. See LSJ s.v.