G4828 συμμαρτυρέω (symmartyréō)

KJV renderings: testify unto, (also) bear witness (with)
Strong's definition: to testify jointly, i.e. corroborate by (concurrent) evidence
Derivation: from G4862 (σύν) and G3140 (μαρτυρέω);

From James Strong's public-domain dictionaries (G), JSON edition by OpenScriptures (CC-BY-SA). Every dotted-underline word in the text links here.