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Cebolinha vs. cebolinha-verde vs. cebolinho

Word practice demo
The terms cebolinho, cebolinha, and cebolinha-verde all refer to plants in the onion family used as herbs or vegetables. The main differences lie in regional usage between Brazil and Portugal, and sometimes in the specific variety of the plant (scallions vs. chives).

Cebolinha

A2
This is the most common term used in Brazil. It refers to scallions or green onions (Allium fistulosum). It is often used in a cheiro-verde bundle alongside parsley. While it is technically the diminutive form of cebola (onion), in a culinary context, it strictly means green onion.
Pique a cebolinha e jogue por cima da sopa.
(Chop the green onions and sprinkle them over the soup.)
Não esqueça de comprar cebolinha para o vinagrete.
(Do not forget to buy scallions for the vinaigrette.)
Eu gosto do sabor fresco que a cebolinha adiciona.
(I like the fresh flavor that green onions add.)

Cebolinha-verde

B1
This is utilized primarily in Brazil as the full, descriptive name for scallions. It is completely synonymous with cebolinha but is slightly more specific, ensuring the listener understands you are talking about the green leaves, not small bulb onions.
A cebolinha-verde deve ser lavada antes do uso.
(The green onions must be washed before use.)
Minha avó planta salsa e cebolinha-verde no quintal.
(My grandmother plants parsley and green onions in the backyard.)
Corte a cebolinha-verde em pedaços pequenos.
(Cut the green onions into small pieces.)

Cebolinho

B1
This usage is standard in Portugal (European Portuguese). It generally refers to chives (Allium schoenoprasum), which are thinner and more delicate than standard green onions, though it can arguably cover spring onions as well depending on the region. In Brazil, this word is rarely used.
Em Portugal, o cebolinho é muito usado em pratos de peixe.
(In Portugal, chives are used a lot in fish dishes.)
Decore o prato com um pouco de cebolinho fresco.
(Garnish the plate with a little fresh chives.)
O cebolinho tem um sabor mais suave que a cebola normal.
(Chives have a milder flavor than normal onions.)

Summary

In summary, use cebolinha or cebolinha-verde if you are in Brazil to refer to scallions/green onions. Use cebolinho if you are in Portugal, where it usually refers to chives.