Usually, the illustration facing title page (in rare cases the illustration could be elsewhere near the front of the book and not necessarily opposite the title page.

1590s, "decorated entrance of a building," from Middle French frontispice (16c.), which is probably from Italian frontespizio and Medieval Latin frontispicium "facade," originally [..]

an illustration or plate inserted immediately in front of the title page, with the illustration facing the title page, often abbreviated as frontis.

an illustration inserted to face the title-page

An illustration or plate inserted immediately in front of the title page, with the illustration facing the title page, often abbreviated as frontis.

In printed books, an unnumbered illustration or pictorial element appearing on the unpaginated verso of the leaf immediately preceding the title page or first page, also found in some Renaissance manu [..]

An illustration facing the title page, or more generally anywhere before the first page of the main text.

(n) an ornamental facade(n) front illustration facing the title page of a book

The first page of a manuscript. Also means the pediment over doors and the gable on top of the middle part of a building.  

This term refers to an illustration directly opposite or preceding the title page of a book.

Illustration in a book opposite the title page.

A term that refers to an illustration directly opposite or preceding the title page of an illuminated book.

(publishing) An illustration that is on the page before the title page of a book, a section of one, or a magazine. (archaic,publishing) The title page of a book. (architecture) A [..]