συναποθνήσκωsynapothnḗskō

to die with or together: Mark 14:31, 2 Corinthians 7:3 (see Meyer, in l.), 2 Timothy 2:11.

Greek (New Testament) · G4880

Same root

σύνsýn · G4862with or together (but much closer than G3326 (μετά) or G3844 (παρά)), i.e. by association, companionship, process, resemblance, possession, instrumentality, addition, etc.
ἀποθνήσκωapothnḗskō · G599to die off (literally or figuratively)

Where it appears

Appears 3 times in the Bible.

Mark 14:31 “No!” Peter declared emphatically. “Even if I have to die with you, I will never deny you!” And all the others vowed the same.
2 Corinthians 7:3 I’m not saying this to condemn you. I said before that you are in our hearts, and we live or die together with you.
2 Timothy 2:11 This is a trustworthy saying: If we die with him, we will also live with him.

Source: G. Abbott-Smith, A Manual Greek Lexicon of the New Testament (1922), public domain.