Alfabeto vs. abecedário
In Portuguese, both alfabeto and abecedário translate to alphabet. However, they are not always interchangeable, as they carry different connotations and are preferred in different contexts. Alfabeto is the standard, universal term, while abecedário often relates to early learning or the fundamentals of a topic.
Alfabeto
A1This is the most common, formal, and neutral word for alphabet. It refers to the established set of letters of a language in its conventional order. Alfabeto is the standard term used in all situations, from academic and technical contexts to everyday conversation.
O alfabeto português tem 26 letras.
(The Portuguese alphabet has 26 letters.)
Ela está a aprender o alfabeto grego para a sua aula de filosofia.
(She is learning the Greek alphabet for her philosophy class.)
O alfabeto fonético internacional é uma ferramenta essencial para linguistas.
(The international phonetic alphabet is an essential tool for linguists.)
A invenção do alfabeto foi um marco na história da comunicação.
(The invention of the alphabet was a milestone in the history of communication.)
Abecedário
B1This word also means alphabet, but its use is more specific and often carries a pedagogical or elementary connotation. Abecedário frequently refers to a primer, a chart, or a song used to teach children their ABCs. It can also be used figuratively to mean the basics or fundamentals of a subject. While it can be a direct synonym for alfabeto, it is far less common in general use and can sound a bit more playful or dated.
A professora colou um abecedário colorido na parede da sala de aula.
(The teacher taped a colorful alphabet chart to the classroom wall.)
O meu primeiro livro foi um abecedário com animais.
(My first book was an alphabet primer with animals.)
Vamos cantar a canção do abecedário todos juntos.
(Let's sing the alphabet song all together.)
A honestidade é o abecedário da confiança.
(Honesty is the ABCs of trust.)
Summary
In essence, use alfabeto as the default, all-purpose word for alphabet. It is always correct. Use abecedário when you specifically want to evoke the context of early childhood education, refer to a physical learning tool like a chart or primer book for teaching letters, or when speaking figuratively about the fundamental principles (the ABCs) of a topic.