Cisco vs. partícula vs. grão vs. grãozinho
While cisco, partícula, grão, and grãozinho all refer to tiny pieces of matter, their usage depends heavily on the context. Cisco usually implies unwanted debris, partícula is scientific, grão relates to granular textures like sand or food, and grãozinho emphasizes tininess.
Cisco
B2This word refers to a tiny bit of unwanted dust, dirt, or debris. It is the most common term used to describe a foreign object irritating the eye.
Entrou um cisco no meu olho enquanto eu andava de bicicleta.
(A speck of dust got into my eye while I was riding my bike.)
Varra o chão até não sobrar nenhum cisco.
(Sweep the floor until there isn't a speck left.)
Ele tirou o cisco da camisa com a mão.
(He brushed the speck of dirt off his shirt with his hand.)
Partícula
B2This is a formal or technical term equivalent to particle. It is used in scientific contexts (physics, chemistry) or when describing air quality and suspension.
O raio de sol revelou milhares de partículas de poeira flutuando no ar.
(The sunbeam revealed thousands of dust specks floating in the air.)
Essa máscara filtra partículas perigosas.
(This mask filters dangerous particles.)
Cientistas descobriram uma nova partícula subatômica.
(Scientists discovered a new subatomic particle.)
Grão
B1Examples of this word include grain or bead. It usually refers to a hard, distinct unit of a substance, such as sand, rice, or minerals.
Tenho um grão de areia no meu sapato que está me incomodando.
(I have a grain of sand in my shoe that is bothering me.)
Ela colocou um grão de pimenta na sopa.
(She put a corn of pepper in the soup.)
A imagem ficou ruim e com muito grão.
(The image turned out bad and with a lot of grain.)
Grãozinho
B1This is the diminutive form of grão. It is used to describe an incredibly small speck or grain, often emphasizing its minuteness or cuteness.
Vi um grãozinho de açúcar em cima da mesa.
(I saw a tiny speck of sugar on top of the table.)
Comprei um brinco com um grãozinho de diamante.
(I bought an earring with a tiny speck of a diamond.)
Adicione apenas um grãozinho de sal.
(Add just a tiny pinch of salt.)
Summary
In summary, use cisco for annoying specks of dirt and specifically for things in the eye. Use partícula for formal descriptions of dust or physics. Use grão for individual pieces of hard substances like sand, and grãozinho when you need to emphasize that the grain is very small.