Wordorigins.org

In today’s speech, tabloid refers to a sensational style of journalism and somewhat more rarely, to a newspaper print format that uses smaller pages and folds like a book (as opposed to broadsheet, the traditional newspaper format). But the term got its start in the field of pharmaceuticals.

Tabloid was registered as a trademark in 1884 by Burroughs, Wellcome & Co. They formed the word by blending tablet with -oid, meaning resembling or similar to. From the Trade Marks Journal of 23 April 1884:

Tabloid...Burroughs, Wellcome & Company, Snow Hill Buildings, Holborn Viaduct, London, E.C....Chemical substances not included in Class I, used in Medicine and Pharmacy.