This article is from the alt.usage.english FAQ, by Mark Israel firstname.lastname@example.org with numerous contributions by others.
"Cocaine" used to be pronounced /'coU cA: in/ (3 syllables).
"Waistcoat" used to be pronounced /'wEskIt/. "Humble" and "human"
were borrowed from French with no [h] in their pronunciation.
"Forte" in the sense "strong point" comes from French "fort"=
"strong, strong point"; the English spelling is what the OED calls
an "ignorant" substitution of the feminine form of the adjective
for the masculine noun. But even in the French feminine form
"forte", the "e" is not pronounced.
"Zoo" is an abbreviation of "zoological garden". The (popular
but stigmatized) pronunciation of "zoological" as /zu:@'lA.dZIk@l/
(as opposed to /zoU@'lA.dZIk@l/) is due to the influence of "zoo".
"Elephant" was "olifaunt" in Middle English, but its spelling was
restored to reflect the Latin "elephantus". Similarly, "crocodile"
"Golf" is Scots. The traditional Scots pronunciation is /gof/.
"Ralph" was traditionally pronounced /reIf/ in Britain -- Gilbert
and Sullivan rhymed it with "waif" in "H.M.S. Pinafore"; that's how
the composer Ralph Vaughan Williams pronounced his name; and even
today actor Ralph Fiennes (of "Schindler's List" fame) is said to
pronounce his name /reIf faInz/.
"Medicine" and "regiment" were two-syllable words in the 19th
century: /'mEdsIn/ and /'rEdZm@nt/. /'mEdsIn/ can still be heard
in RP. In 19th-century England, "university" was pronounced
/,ju:nIv'A:sItI/ and "laundry" was pronounced /'lA:ndrI/.
King Arthur would have pronounced his name /'artur/. The h's in
"Arthur" (now universally reflected in the pronunciation) and
"Anthony" (reflected in the U.S. pronunciation) were added in the
15th century -- ornamentally or, in the case of "Anthony", because
of a false connection with Greek "anthos"="flower".
The new pronunciations in such cases are called "spelling
pronunciations". The "speak-as-you-spell movement" is described in
the MEU2 article on "pronunciation".