Lexical Definition

‎κατήγορος‎ katḗgoros (kat-ay'-gor-os) accuser ^G:N-M
from ‎κατά‎ and ‎ἀγορά‎

accuser.

• against one in the assembly, i.e. a complainant at law
• specially, Satan

Abbott-Smith

κατήγορος, -ου, ὁ, [in LXX: Pr 18:17 (ריב), II Mac 4:5*;]
an accuser: Ac 23:30, 35 24:8 (WH, R, txt. om.) Ac 25:16, 18.†

Abbott-Smith References

Liddell-Scott-Jones

κατήγορος-ος, ὁ,

accuser, [NT+5th c.BC+]; δημόσιος κ. public prosecutor, [Refs 3rd c.AD+]; betrayer, φρονημάτων ἡ γλῶσσ᾽ ἀληθὴς γίγνεται κ. [Refs 5th c.BC+]; πνεῦμα ὧν κατήγοροςον,.. δρόμοις [ἡ φύσις] ἐκβιᾶται κατηγορέειν what the respiration reveals, [Refs 5th c.BC+]

_{LSJ Scripture Refs: Rev.12.10}