Brazilian Portuguese Grammar

3. Proper names of rivers, oceans, seas and lakes are masculine:

O Oceano Atlântico	The Atlantic Ocean	O Oceano Pacífico	The Pacific Ocean
O Mar Mediterrâneo	The Mediterranean Sea	Os Grandes Lagos	The Great Lakes
O Mar Morto	The Dead Sea	O Rio Amazonas	The Amazon River
O Rio Tâmisa	The Thames River	O Lago Titicaca	Lake Titicaca

4. Proper names of mounts and mountains: with the words monte (mount) or pico (peak), they are masculine; with the words montanha (mountain), serra or cordilheira (mountain range), they are feminine:

O Evereste	Mount Everest	As Montanhas Rochosas	The Rocky Mountains
O Monte Sinai	Mount Sinai	A Serra Nevada	Sierra Nevada

Note the following names:

Os Alpes	The Alps
Os Bálcãs	The Balkans
A Cordilheira dos Andes or Os Andes	The Andes

5. The days of the week are feminine, except sábado and domingo, which are masculine:

a segunda-feira	Monday
a terça-feira	Tuesday
a quarta-feira	Wednesday
a quinta-feira	Thursday
a sexta-feira	Friday
o sábado	Saturday
o domingo	Sunday

6. The cardinal points are masculine:

o norte	the north
o sul	the south
o leste	the east
o oeste	the west
o nordeste	the northeast
o sudeste	the southeast
o noroeste	the northwest
o sudoeste	the southwest
o centro-oeste	the midwest

7. All language names are masculine:

o português	Portuguese
o inglês	English
o francês	French
o japonês	Japanese
o alemão	German
o espanhol	Spanish
o latim	Latin
o grego	Greek
o russo	Russian
o árabe	Arabic
o hebraico	Hebrew
o dinamarquês	Danish
o holandês	Dutch
o chinês	Chinese
o coreano	Korean
o italiano	Italian

8. Country names:

Ending in -o, -ão are masculine;
Ending in -a, -ã are feminine;
Ending in -e, -i, -l, -le, r are also masculine;
Ending in á (a with an acute accent) are masculine.

a França	France
a Alemanha	Germany
a Itália	Italy
a Argentina	Argentina
a Irlanda	Ireland
a Austrália	Australia
o Chile	Chile
o Chipre	Cyprus
o Brasil	Brazil
os Estados Unidos	The United States
o Japão	Japan
o Canadá	Canada
o Panamá	Panama
a Coréia do Norte	North Korea
o Egito	Egypt
o Iraque	Iraq
a Nigéria	Nigeria
o Equador	Ecuador
o México	Mexico
a Turquia	Turkey
a Indonésia	Indonesia
o Haiti	Haiti
o Uruguai	Uruguay

Note:

The definite articles (o, os, a, as) aren't used before the following country names:

Israel	Israel
Cuba	Cuba
Cingapura	Singapore
Honduras	Honduras
Portugal	Portugal
Omã	Oman
Uganda	Uganda
Ruanda	Rwanda
Moçambique	Mozambique

Click here to get information on the use of definite articles with Brazilian states.