Which is the correct spelling; ketsup, ketchup or catsup, and why three different spellings?

Ketchup appears to be the popular decision.

The variations are based upon the originating geographical area...India, China, etc.

https://www.mentalfloss.com/article/29649/whats-difference-between-ketchup-and-catsup

As is the case for many words that have their linguistic roots in an Asian language, the spelling in English varies with the way in which the Asian word gets translitereted. While the wikipedia article at the link is titled catsup, it redirects to ketchup, the spelling which is used within the article. The word is thought to have its origins possibly in a Chinese word that can be transliterated as ke-tep or kio-chiap. Alternatively, it may derive from a Malay word spelled variously kicap, kecap, ketjap. Its first use in english is recorded in 1690 as catchup; ketchup appears in 1711, and catsup in 1730.

https://en.wikipedia.org/wiki/Catsup


The Online Etymoligical Dictionary suggests that catsup, cetchup (which I have never seen!); and ketchup are all accepted alternative spellings. (A bit like grey and gray.)

http://www.thefreedictionary.com/catsup

"In the 1980's ketchup was declared a vegetable by the government for school lunch menus." Now that's WRONG!

The American choice of ketchup as the spelling for the reasons outlined is not international. Although ketchup is the most commonly seen in Australia, (if it's not labeled as Tomato Sauce), catsup does also appear. Neither of them has legally been given a status of preference, so it really just depends on the brand here.

http://www.statsci.org/smyth/ozus.html

"Ketchup or Catsup?

"When Heinz introduced commercial ketchup to American kitchens it became so popular that other manufacturers rushed to catch-up to the ketchup craze. Soon there were Ketchup, Catsup, Catchup, Katsup, Catsip, Cotsup, Kotchup, Kitsip, Catsoup, Katshoup, Katsock, Cackchop, Cornchop, Cotpock, Kotpock, Kutpuck, Kutchpuck and Cutchpuck. All were tomato based and bottled and vied to become a household word. Only 3 major brands remained to steal the spotlight...Heinz Ketchup, Del Monte Catsup, and Hunts, who could not decide on a spelling and bottled under the names Hunts Catsup (east of the Mississippi), Hunts Ketchup (west of the Mississippi), and Hunts Tomato Cornchops (in Iowa only). In the 1980's ketchup was declared a vegetable by the government for school lunch menus. Suddenly Del Monte's Catsup, because of its spelling, was not on the approved list. Shortly afterward Del Monte changed the product's name to Del Monte Ketchup. So ketchup it is."

http://www.globalgourmet.com/food/sleuth/0799/

Actually, "In the 1980's ketchup was declared a vegetable by the government for school lunch menus," IS wrong! Even though it's all over the internet.

The Reagan administration proposed it for the well-intended reason of serving what kids would eat so as to avoid the waste of throwing out vegetables they were served but wouldn't eat. The proposal did not pass, and the government looked silly.

http://www.straightdope.com/columns/read/2517/did-the-reagan-era-usda-really-classify-ketchup-as-a-vegetable