[IRMartin]

Curiously, Portuguese is the one of the few European languages that 'depaganized' the name of the days due to a missionary from Constantinople.
St. Martin of Dume was born in Panonia and was educated in Constantinople. He became missionary in Lusitania and Archbishop of the See of Braga, the oldest of Portugal. In true Orthodox Tradition, he was the first to translate to Latin the Sayings of the Desert Fathers. He presided over two local councils and fought the heresy of priscilianism ( http://mb-soft.com/believe/txc/priscill.htm ).

In his mission to convert the Suevs and other local pagans, he changed the name of the days. Thus:

Sunday - Domingo (from Latin "Domine")
Monday - Segunda-Feira (Second Fair)
Tuesday - Terça-Feira (Third Fair)
Wednesday - Quarta-Feira (Fourth Fair)
Thursday - Quinta-Feira (Fifth Fair)
Friday - Sexta-Feira (Sixth Fair)
Saturday - Sábado (from Sabbath)

Also Christmas is Natal, from Nativity and Easter is Páscoa.

He also intended to change the names of the planets but unfortunately either he did not come up with names or it did not stick. :P