Strong's G2649 — καταμαρτυρέω (verb)
katamartureo (kat-am-ar-too-reh'-o) v.
1. to testify against
[from G2596 and G3140]
KJV: witness against 
Root(s): G2596, G3140 
Hebrew root: μαρτυρέω
Occurrences: 3