The word used is συνάφεια, a crucial word in the controversy concerning the union of the divine and human natures in our Lord, cf. the third Anathema of Cyril against Nestorius and the use of this word, and Theodoret’s counter statement (Theod. pp. 25, 27).  Theodore of Mopsuestia had preferred συνάφεια to ἕνωσις; Andrew of Samosata saw no difference between them.  Athanasius (de Sent. Dionys. § 17) employs it for the mutual relationship of the Persons in the Holy Trinity:  “προκαταρκτικὸν γάρ ἐστι τῆς συναφείας τὸ ὄνομα.”