Cotonou is named from the local Fon language where the name originally meant 'river of death', this being the Oueme River.
Porto-Novo is a name of Portuguese origin and describes 'the new port', although it has not been 'new' since renamed by them in the 16th century.
Parakou is a Dendi word meaning La ville de tout le monde, a reminder this had been French territory, indeed once known as French Dahomey, and refers to 'the city of everyone'. Incidentally the name of Dahomey is discussed under my earlier blog
Bohicon is a modern form of the correct name of Gboxicon, literally meaning 'market sheep' and accurately describing the major commodity fuelling the economy of the city.
Note the spellings of the places are English as the piece is written in English.