Introductory, a.
Etymology: [L. itroductorius: cf. F. introductoire.]
Serving to introduce something else; leading to the main subject or business; preliminary; prefatory; as, introductory proceedings; an introductory discourse.
Shades of meaning
Fernald has no entry of its own for introductory; he lists it under previous.
He lists it without comment; the entries above explain its neighbors.