It looks like I was deceived. The bit about Mavros deriving from an African language is on
http://www.takeourword.com/TOW189/page2.html Funny enough, they also mention the Oxford English dictionary as their source. But it's certainly not in the edition I have! I should have been more sceptical, because I did notice that they think that Morocco also derives from Mavros, and it definitely does not...
Regards,
Obie