What is "great primer"

Primer \Prim"er\, n. [Originally, the book read at prime, the first canonical hour. LL. primae liber. See Prime, n., 4.]

1. Originally, a small prayer book for church service, containing the little office of the Virgin Mary; also, a work of elementary religious instruction.

   The primer, or office of the Blessed Virgin.
   --Bp. Stillingfleet.

2. A small elementary book for teaching children to read; a reading or spelling book for a beginner.

   As he sat in the school at his prymer.
   --Chaucer.

3. (Print.) A kind of type, of which there are two species; one, called long primer, intermediate in size between bourgeois and small pica [see Long primer]; the other, called great primer, larger than pica.

   Note: Great primer type.

Great primer is a large font size (18 points) that was used in the printing of English Bibles and other large-format books, leading to its other name of Bible Text. The largest size ever (or at least up to about 1843) used in England for printing books, it was several sizes larger than English (14 pt) but smaller than paragon (20 pt). It was known in Italian as testo. Other synonyms include Double Bourgeois, 18-point, Gros Romain (French), Text (Dutch) and Tertia (German).

Great-primer size fonts have been in use since William Caxton, around 1488.