Lyric discussion by Digi-G 

Cover art for Mamunia lyrics by Paul McCartney

I always assumed the work Mamunia was either slang (I've never heard it) or possibly a term from Nigeria where the Band on the Run album was recorded. Because of this song I've assumed it means 'rain'. Lyrically it's almost a remake of the Beatles 'Rain' - musically it doesn't sound anything like it.