The 90th Scripps National Spelling Bee kicked off on Wednesday with nearly 300 young spellers from around the country gunning for a $40,000 top prize.

The field of 291 children will be whittled down to one champion at Thursday's final in Oxon Hill, Maryland.

Since the inaugural competition in 1925, the words featured in the bee have become increasingly more difficult and obscure, requiring participants to have a commanding knowledge of root words, etymology, and world languages.

Scripps's list of "winning words" from previous competitions gives a glimpse at this evolution. Relatively simple words such as "knack," "therapy," and "initials" dominated earlier installments of the spelling bee, while modern-day champions have had to tackle humdingers like "feuilleton," "nunatak," and "gesellschaft."

The shift in difficulty can be partly attributed to ESPN's coverage of the bee, which has attracted more students to the competition, Scripps spokeswoman Valerie Miller said. This is the 24th year ESPN will air the spelling bee.

But the biggest reason is simply that the spellers have gotten better.

"Words are more difficult now because the skills of the students also have expanded," Miller told Business Insider. "These are the best of the best spellers, and the words they get in the national finals should be the greatest challenge."

Here are some of the championship-clinching words from previous spelling bees:

1925 — gladiolus

The championship word from the inaugural National Spelling Bee in 1925 was "gladiolus," a flowering plant in the iris family.

Eleven-year-old Frank Neuhauser of Kentucky correctly spelled it to take home the top prize — $500 in gold pieces and a trip to the White House.

When he returned to Louisville, crowds greeted him with a ticker-tape parade and bouquets of aptly chosen gladiolus flowers, according to The Washington Post's obituary of Neuhauser, who died in 2011.

The New York Times called Neuhauser's winning word "a cakewalk by modern standards" that "

In the photo to the right, sixth-place finisher Patrick Kelly poses with President Calvin Coolidge.

1936 — eczema

Jean Trowbridge of Iowa correctly spelled "eczema" — a skin condition — to clinch the 1936 spelling bee. She also had to correctly spell "predilection," which another finalist had missed.

Three decades later, "eczema" would resurface as the winning word at the 1965 bee.

1960 — eudaemonic

Henry Feldman of Tennessee correctly spelled "eudaemonic" to win the 1960 spelling bee. "Eudaemonic" means "producing happiness."

1967 — chihuahua

Jennifer Reinke of Nebraska clinched the 1967 title by correctly spelling "chihuahua." The dog breed shares its name with the Mexican state it originates from.

1970 — croissant

Libby Childress of North Carolina aced the word "croissant" to win the 1970 title.

1978 — deification

"Deification" was the winning word at the 1978 spelling bee, correctly spelled by Peg McCarthy of Kansas.

"Deification" is the act of treating someone like a god.

1987 — staphylococci

By the mid-1980s, the words used in the spelling bee finals became dramatically more difficult. Stephanie Petit of Pennsylvania won the 1987 bee by spelling "staphylococci," the plural form of a type of disease-causing bacteria.

1998 — chiaroscurist

Jody-Anne Maxwell of Jamaica won the 1998 spelling bee, becoming the first non-American champion in the event's history.

Maxwell clinched the championship by spelling "chiaroscurist," a painter who uses shadows and exaggerated light contrasts for artistic effect.

2005 — appoggiatura

San Diego's Anurag Kashyap won the 2005 spelling bee by spelling "appoggiatura," a word for an embellishing musical note.

2011 — cymotrichous

Sukanya Roy of Pennsylvania won the 2011 spelling bee by correctly spelling "cymotrichous," a way to describe wavy hair.

2015 — scherenschnitte, nunatak

Two spellers were named co-champions in 2015 after the finalists exhausted the entire list of words.

Vanya Shivashankar of Kansas correctly spelled "scherenschnitte" — the art of paper cutting — to earn her share of the title.

Missouri's Gokul Venkatachalam clinched with an equally obscure word — "nunatak," a word of Greenlandic origin referring to a hill or mountain completely surrounded by glacial ice.

2016 — Feldenkrais, gesellschaft

Last year's spelling bee saw another tie after finalists exhausted the entire word list.

The two winning words were "Feldenkrais," spelled by Jairam Hathwar of New York, and "gesellschaft," spelled by Nihar Sai Reddy Janga of Texas.

"Feldenkrais" is a type of exercise therapy devised by Israeli engineer Moshe Feldenkrais. "Gesellschaft," in social theory, is a word for a society in which human relations are impersonal.

And here's the list of every winning word since 1925:

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