Brazilian Portuguese Grammar

21. The so-called substantivos comuns de dois gêneros have the same form for the masculine and the feminine gender, but determiners (articles, pronouns) accompanying them make the gender clear:

o agente a agente	the agent
o jornalista a jornalista	the journalist
o repórter a repórter	the reporter
o policial a policial	the police officer
o jovem a jovem	the young man the young woman
o estudante a estudante	the student
o imigrante a imigrante	the immigrant
o gerente a gerente	the manager

Note: All nouns ending in -ista are substantivos comuns de dois gêneros: o cientista/ a cientista (the scientist) - o filatelista/ a filatelista (stamp collector), etc.

22. The following nouns have completely different forms for the masculine and the feminine:

Masculine	Feminine
o homem - the man	a mulher - the woman
o pai - the father	a mãe - the mother
o padrinho - the godfather	a madrinha - the godmother
o marido - the husband	a esposa / a mulher - the wife
o bode - the billy-goat	a cabra - the nanny-goat
o boi - the ox	a vaca - the cow
o galo - the rooster	a galinha - the hen
o cachorro - the dog	a cadela - the female dog
o cavalo - the horse	a égua - the mare
o carneiro - the ram	a ovelha - the sheep
o zangão - the drone	a abelha - the bee
o genro - the son-in-law	a nora - the daughter-in-law
o rei - the king	a rainha - the queen

23. Other masculine nouns take suffixes such as -esa, -essa, -ina, -isa and -iz to form the feminine:

Masculine	Feminine
o conde - the earl	a condessa - the countess
o príncipe - the prince	a princesa - the princess
o duque - the duke	a duquesa - the duchess
o barão - the baron	a baronesa - the baroness
o imperador - the emperor	a imperatriz - the emperess
o maestro - the orchestra conductor	a maestrina - the orchestra conductor
o profeta - the prophet	a profetisa - the prophet
o sacerdote - the priest	a sacerdotisa - the priestess
o poeta - the poet	a poetisa - the poetess
o tigre - the tiger	a tigresa - the tigress

24. Most names of animals are epicenos, that is, you need to use the words macho (male) and fêmea (female) to ascertain the gender:

English	Masculine	Feminine
the fly	a mosca macho	a mosca fêmea
the alligator	o jacaré macho	o jacaré fêmea
the whale	a baleia macho	a baleia fêmea
the shark	o tubarão macho	o tubarão fêmea
the snake	a cobra macho	a cobra fêmea
the butterfly	a borboleta macho	a borboleta fêmea
the turtle	a tartaruga macho	a tartaruga fêmea

Note: You could say this is the rule to ascertain the gender of insects, reptiles, birds and amphibians.