This is a jokey journalists’ term for that group of people whose job is to comment on the news. It seems to have first appeared in the US in the early nineties but only to have become fashionable in about 1997. It’s found often enough to suggest that it may be here to stay. It remains closely associated with political and media circles in the USA; when it appears in other countries, it is mostly in reference to American political affairs. William F Buckley, writing in the Sacramento Bee in October 1997, defined it as “the name given to talk-show hosts who opine on the Sunday shows”, but its scope is wider than that, encompassing all those experts, pundits and pollsters who analyse political events and discuss their implications. The word is a punning clipped blend of commentator with the suffix -ariat, a moderately rare ending derived from French which denotes an office or function (it’s equivalent to one sense of the English suffix -ate, as in directorate or professorate). The immediate inspiration was probably one or other of proletariat or commissariat (in the old Russian governmental sense rather than the military food-providing one), with a nod towards secretariat.
Even before the recent reports, the commentariat had embraced a new national parlor game: devising ways for Clinton to extricate himself from Grand Jury Jeopardy.
Washington Post, Aug. 1998
Although Lott was eventually reined in (by Jesse Helms, of all people), that word “timing” became the mantra of the right-leaning half of the commentariat.
Pilot-Independent (Walker, Minnesota), May 1999