In the context of Banach space theory, what is the correct terminology: *extremally* disconnected or *extremely* disconnected. Looking through the internet I have met using both [extremely](https://math.stackexchange.com/questions/1808481/proof-that-ck-is-a-grothendieck-space-for-k-an-extremely-disconnected-comp) and [extremally](https://math.stackexchange.com/q/128388) disconnected. Or is there a difference between those two notions?



Extremely disconnected or extremally disconnected?
The correct word is **extremally** (which is not in standard English) and is indeed often mistakenly corrected to the more common "extremely" — possibly, in recent case, with the unfortunate help of automatic correctors. Extremely would mean "very very", while "extremally" purports to mean, as far as I understand "in an extremal way".


An MSN search *anywhere* = "extremally disconnected" vs "extremely disconnected" with "year $<$ 1963" yields 24 papers vs 1 paper (note that this mostly detects the spelling of the MSN review, although when misspelled it fitted the spelling of the paper in a few cases I checked). Without the year restriction (say, with year $<2021$, to fix things) it yields 600 papers vs 64 papers. In Google Scholar, the only few occurrences before 1950 are with "extremally disconnected" (I tried to open [a 1943 paper by Hewitt](https://doi.org/10.1215/S0012-7094-43-01029-4) but instead noticed along the way that Duke Math J. still likes to get our money out of 80 years old papers).


