Borrowed from Latin pīca (“jay; magpie”). Doublet of pie (“magpie”).
* (pathology): From the idea that magpies will eat almost anything.
Meanings
(uncountable, usually) A disorder characterized by appetite and craving for non-edible substances, such as chalk, clay, dirt, ice, or sand.
The three most common nonfood picas were eating of strings and rags; feces, vomit, and urine; and paper, cigarettes, and soil. 1986, George S Baroff, Mental retardation: nature, cause, and management:
From Medieval Latin pica (“pica: a service book”), possibly from Latin pīca (“magpie”) after the piebald appearance of the typeset page (cf. pie (“disordered type”)). The relation to the printer's measure is unclear, as no edition of the text in pica type is known. The French pica derives from English rather than vice versa.
Meanings
(uncountable) A size of type between small pica and English, now standardized as 12-point.
The difference to you of treacle on a marble background is scarcely greater than that of printers' ink on newspaper to me. But anything smaller than pica I do not read with comfort, and below long primer I cannot read at all. 1914, Ernest Bramah, Max Carrados:
I had been at Baldwin's before dinner in consequence of a letter from him which showed me that, by using a pica instead of an English letter in printing my book, I might comprise it within such a number of sheets as a guinea-volume should contain […]. 1790, James Boswell, edited by Danziger & Brady, Boswell: The Great Biographer, Yale, published 1989, page 30:
(uncountable, usually, with qualifier) A font of this size.
(countable) A unit of length equivalent to 12 points, officially ³⁵⁄₈₃ cm (0.166 in) after 1886 but now (computing) ¹⁄₆ in.
(countable, uncommon, uncountable) A pie or directory: the book directing Roman Catholic observance of saints' days and other feasts under various calendars.
Most travellers in the Himalaya are familiar with the pretty little Rodents, known as picas, tailless hares, or mouse-hares, which may be seen in the higher regions[…] 1895, Richard Lydekker, The Royal Natural History, volume 3, page 190: