People words with fixed grammatical gender
In Portuguese, every noun has a gender. Usually, nouns referring to people change gender to match the person you are talking about, giving us pairs like o menino for a boy and a menina for a girl. However, there is a special group of nouns referring to people that have a permanently fixed grammatical gender.
These are fixed-gender nouns. Words like a pessoa or a criança are always feminine, even if you are talking about a man or a boy. English speakers often trip over this because our instinct is to change the adjectives to match the person's biological gender. In Portuguese, the articles and adjectives used with the noun must strictly follow the noun itself.
The most common fixed-gender words you will encounter are pessoa, criança, and ser humano. Because pessoa and criança are grammatically feminine, any articles and adjectives you attach directly to these nouns must also be feminine. This applies even when you are talking about a man. Conversely, ser humano is always masculine, even when describing a woman.
Legal terms and official roles often function the same way. Words like vítima and testemunha are permanently feminine. Meanwhile, indivíduo and the formal word for spouse, cônjuge, are permanently masculine.
If a woman is the victim, she is a vítima. If a man is the victim, he is also a vítima. All adjectives attached to the word must be feminine.
Terms used for fame, specific types of people, and metaphors also follow this strict rule. Estrela, estrela de cinema, celebridade, and criatura are always feminine. On the masculine side, we have words like gênio, fantoche, and bode expiatório.
When using a fixed-gender noun to describe a person, your articles and adjectives must agree with the grammatical gender of the word itself. You must ignore the biological gender of the person you are talking about.