Nouns that are masculine by form
从形式上判断是阳性的名词
(i) The vast majority of nouns ending in -o are masculine.
绝大部分以-o结尾的名词都是阳性的
Exceptions: nouns ending in -ção/-são that correspond to English nouns ending in -tion/-sion; the words mão ‘hand’ and tribo ‘tribe’, and words ending in –o that are abbreviations of longer feminine nouns such as foto ‘photo’ (from fotografia) and moto ‘motorcycle’ (from motocicleta).
例外：以-ção/-são结尾（对应英语上的词尾-tion/-sion），ão ‘hand’‘手’ 和 tribo ‘tribe’‘部落’，那些以-o结尾的阴性名词的缩写，例如，foto ‘photo’‘图片’ (缩写自 fotografia)
moto ‘motorcycle’‘摩托车’ (缩写自motocicleta).
(ii) In addition, nouns with the following endings are masculine: -ão (when referring to a male human being or an inanimate object), e.g. cidadão ‘citizen’, cartão ‘card’;
-dor/-tor, e.g. cantor ‘singer’, traidor ‘traitor’; -ma when the English cognate ends in -m or -ma, e.g. dilema ‘dilemma’, sistema ‘system’.
除此之外，以下面作为词尾的名词都是阳性的
以-ão结尾的名词（当涉及到的是雄性的人类或者是生命的事物时候）。例如. cidadão ‘citizen’‘公民’, cartão ‘card’‘卡片’，
以-dor/-tor结尾的，例如，cantor ‘singer’，‘歌手’, traidor ‘traitor’，‘叛徒’;
以-ma结尾的，英语词源上以-m 或者 -ma结尾的，例如 dilema ‘dilemma’，‘困境’, sistema ‘system’，‘系统’.