Amanuensis: A person, such as a scribe or secretary, hired to write from dictation or from a brief outline of a letter (from Latin manu, “hand”).
Tertius is named the “writer” of Romans (16:22). Paul also employed other individuals, and he draws attention to the fact by commenting that he is closing the letter in his own hand (cf. 1Cor 16:21; Gal 6:11; Col 4:18; 2 Thess 3:17). Silvanus is identified as Peter’s amanuensis (1 Pet 5:12).
This practice of using secretaries (see Jer 36:4) may account for some differences in style and language in some of the NT letters attributed to Paul and Peter.
Patzia & Petrotta, Pocket Dictionary of Biblical Studies (2002), 9-10.