I just discovered a very interesting etymology that has apparently been developed only recently. The OED says the origin of calypso (the name of an Afro-Caribbean style of satirical song) is unknown; Webster’s Third New International (1961) says “probably after Calypso, island nymph.” But Richard Allsopp’s superb Dictionary of Caribbean English Usage (1996) has the following etymology:
[ < Efik ka isu ‘go on!’, also KID Ibibio kaa iso ‘continue, go on’, a common phrase used in urging sb on or in backing a contestant. The Efik-Ibibio being the established middlemen in the slave trade (ex at Calabar) the slaves of other ethnic groups would have brought this item (as they did BAKRA) to the CarA as part of the private vocabulary of slave life. In the context of CarA plantation-life, crowds backed creole teasing-songs against MASSA shouting ‘Ka iso!’ wh gradually lost its original meaning. Kaiso is still the regular ECar folk name, not calypso. The phonological development /ka-iso > kariso > kaliso/ is attested by KARISO (Dmca, etc), KARUSO (USVI), and KALISO (StLu) this last recognized as ‘another form ‘Calisseaux’ … in use at the same time as ‘Carisseaux’ ‘ —(Espinet & Pitts, Land of the Calypso, 1944, p. 47). The development > calypso is through corruption (through folk etym) by English writers in the 1930s, influenced by the name (Calypso) of the amorous island nymph of Greek mythology, plus an anglicized shift in pitch pattern /1’12/ > /1’21/]
Most of the abbreviations should be self-explanatory, but CarA is “Caribbean area” and KID in the first line is Elaine Kaufman’s Ibibio Dictionary (Leiden, 1985). The key to the etymology is the recognition that the original form is kaiso; I love the fact that the transmogrification to the highfalutin “calypso” is called, quite properly, folk etymology—the ignorant “folk” aren’t always poor and unlettered! And the careful discussion of how the African form would have reached the Caribbean and been preserved should be a model for such things (there are far too many silly African pseudo-etymologies floating around out there).
The entry in Merriam-Webster’s Collegiate says “Trinidad English, alteration of kaiso, perhaps ultimately of Afr origin”; the caution is probably appropriate for a general-usage dictionary, but personally, I’m provisionally convinced by the Efik-Ibibio etymology.