Index Patristicus Clavis Patrum Apostolicorum Operum

In this important reference work, edited by Goodspeed, several scholars have indexed the Greek and Latin words from early works of the Church, including 1 Clement, 2 Clement, Epistle of Barnabas, Papias, Epistle to Diognetus, Letters of Ignatius, Letter of Polycarp to Philip, Martyrdom of Polycarp, Shepherd of Hermas, and Didache.