An "enchiridion" is a manual or primer. Interestingly, in both ancient and modern Greek, ἐγχειρίδιον / εγχειρίδιο also means "dagger." Because both a small manual and a dagger were things that could fit comfortably in (εγχ / εν) your hand (χείρ / χέρι).

Not all that relevant to Epictetus, just wanted to add a little linguistic note.