A full plan of a thing before the thing exists. Detailed enough to build from, and not itself the building.
A 19th-century compound: blue (Old French bleu) + print (Old French preinte, from Latin premere, to press); named for the cyanotype process patented in the 1840s, whose copies came out as white lines on a deep blue ground.
A full plan of a thing set down before the thing exists, detailed enough to build from and never mistaken for the building itself.