οἱ τότε ἤρχοντο εἰς τὴν νῆσον → they were then coming to the island
subs.
Putting together: P. and V. σύνθεσις, ἡ.
Mixing: P. and V. κρᾶσις, ἡ.
Political association: P. ἐταιρεία, ἡ, σύστασις, ἡ, Ar. and P. σύνοδος, ἡ.