Malagasy (noun and adjective)
is the name of the people and of the language.
Madagascar is the name of the island in English, French,
and a number of other languages.
Madagasikara is the name of the island in Malagasy.
Repoblikan'i Madagasikara,
Republic of Madagascar,
République de Madagascar, are the official names of
the government in Malagasy, English, and French respectively.
Malgache is the French word for Malagasy.
Madécasse is an obsolete French word,
synonym of Malagasy.
Madagascan is used by writers
who need an adjective and
don't know about Malagasy.