συμμέτοχοςsymmétochos

partaking together with; as as a noun, ὁ σ., a joint partaker: with genitive of thing, Ephesians 3:6; with genitive of person, Ephesians 5:7.

Greek (New Testament) · G4830

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.
μέτοχοςmétochos · G3353participant, i.e. (as noun) a sharer; by implication, an associate

Where it appears

Appears 2 times in the Bible.

Ephesians 3:6 And this is God’s plan: Both Gentiles and Jews who believe the Good News share equally in the riches inherited by God’s children. Both are part of the same body, and both enjoy the promise of blessings because they belong to Christ Jesus.
Ephesians 5:7 Don’t participate in the things these people do.

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