Encyclopaedia

Encyclopaedia is the usual spelling in British English. In American English, it is spelled encyclopedia. The British spelling is more consistent, if not accurately so, with the etymology: the word is from late Latin encyclopædia. This in turn derives from the Greek έγκυκλοπαιδεία, so should perhaps be rendered encyclopaidia;. But it isn't, either in British nor in American English. In American Engliszh, following Webster's reforms of spelling, it is always written encyclopedia with no internal '-a-'.

Etymological note: "an erroneous form (said to be a false reading) occurring in MSS. of Quintilian, Pliny, and Galen, for έγκυκλοπαιδεία '˜encyclical education', the circle of arts and sciences considered by the Greeks as essential to a liberal education" (OED, 1891).

Diderot

Denis Diderot, (1713–84)

"It suffices to read some of the analyses of the current dictionaries and encyclopedias (see, for instance, Weinreich 1980; Rey-Debove 1971) to realize that, if so-called encyclopedias are in some way encyclopedic, so-called dictionaries are rather impoverished encyclopedias" (Eco, Semiotics and the Philosophy of Language, Indiana University Press, 1986).