Fairly vs Extremely - What's the difference?

As adverbs the difference between fairly and extremely

is that fairly is in a fair manner; clearly; openly; plainly; fully; distinctly; frankly while extremely is (degree) to an extreme degree.

fairly

English

Adverb

(en adverb)

In a fair manner; clearly; openly; plainly; fully; distinctly; frankly.

Favorably; auspiciously; commodiously.

Honestly; properly.

*1859 , Alexander Easton, A Practical Treatise on Street or Horse-Power Railways , p.108, "Rules adopted by the Sixth Avenue Railway, N. Y.":

*:10. You will be civil and attentive to passengers, giving proper assistance to ladies and children getting in or out, and never start the car before passengers are fairly received or landed.

*:They burned the old gun that used to stand in the dark corner up in the garret, close to the stuffed fox that always grinned so fiercely. Perhaps the reason why he seemed in such a ghastly rage was that he did not come by his death fairly . Otherwise his pelt would not have been so perfect. And why else was he put away up there out of sight?—and so magnificent a brush as he had too..

Softly; quietly; gently.

Partly, not fully; somewhat.

*, chapter=3

, title= Mr. Pratt's Patients , passage=My hopes wa'n't disappointed. I never saw clams thicker than they was along them inshore flats. I filled my dreener in no time, and then it come to me that 'twouldn't be a bad idee to get a lot more, take 'em with me to Wellmouth, and peddle 'em out. Clams was fairly scarce over that side of the bay and ought to fetch a fair price.}}

*{{quote-magazine, date=2013-08-03, volume=408, issue=8847, magazine=(The Economist)

, title= Yesterday’s fuel , passage=The dawn of the oil age was fairly recent. Although the stuff was used to waterproof boats in the Middle East 6,000 years ago, extracting it in earnest began only in 1859 after an oil strike in Pennsylvania. The first barrels of crude fetched $18 (around $450 at today’s prices). It was used to make kerosene, the main fuel for artificial lighting after overfishing led to a shortage of whale blubber.}}

Usage notes

* This is a non-descriptive qualifier'', similar to quite and rather and somewhat, and some other degree adverbs. Used where a plain adjective needs to be modified, but cannot be qualified. When spoken, the meaning can vary with the tone of voice and stress. ''He was fairly' big can mean anything from "not exactly small" to "almost huge".