1884, Tabloid, "small tablet of medicine," trademark name (by Burroughs, Wellcome and Co.) for compressed or concentrated chemicals and drugs, a hybrid formed from tablet + Greek-derived suffix -oid.

A new and successful remedy has been found for the distressing nervous complaint known as hay fever. One-sixth of a grain of the recently discovered remarkable anæsthetic cocaine is incorporated into what are called tabloids and inserted in the nasal passages. [South Branch (W. Va.) Intelligencer, Oct, 30, 1885]

 By 1898, it was being used figuratively to mean a compressed form or dose of anything, hence tabloid journalism (1900), simplified and, in the negative view, sensationalized, and tabloid (n.) in reference to newspapers that typified it (1901).

The concept and word were associated originally with British publishing magnate Alfred C. Harmsworth (1865-1922), editor and proprietor of the London Daily Mail. Harmsworth's use was in reference to the short, condensed news articles; by others it might be felt as referring to the newspaper itself being smaller than a broadsheet.

"What a person wants in his daily morning paper not long-winded essays, nor does he care to have undigested news by the column. He prefers it in concentrated tabloids, with all the interesting points put prominently forward, so that he can run and read." [quoted in Victoria (Australia) Age, Jan. 29, 1898]

1969, short for tab key (1916) of a typewriter (later computer); a short form of tabulator. As "pill, lozenge" it is by 1961, shortened form of tablet (in the later 1960s and after especially one of sugar containing LSD). As an abbreviation of tabloid (newspaper) it is 1990s slang. As a short form of tabulator key of a typewriter (later computer) it is recorded from 1916.