die Partikel
particle
A very small piece of matter, such as a speck of dust, an atom, or an electron.
Nach der Explosion schwebten feine Russpartikel in der Luft.
After the explosion, fine soot particles floated in the air.

particle
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particle
A very small piece of matter, such as a speck of dust, an atom, or an electron.
Nach der Explosion schwebten feine Russpartikel in der Luft.
After the explosion, fine soot particles floated in the air.

You can recognize the meaning from the context. If it is about natural sciences (physics, chemistry), it refers to small particles of matter. If it is about language and grammar, it refers to the part of speech.
Der Filter entfernt selbst kleinste Partikel aus dem Wasser.
The filter removes even the smallest particles from the water.
Both meanings of the word 'Partikel' (particle) are used mainly in technical or scientific contexts.
Die Forscher untersuchen die Wechselwirkung subatomarer Partikel.
The researchers are studying the interaction of subatomic particles.
In a scientific context, 'Partikel' (particle) is often used with adjectives like 'fein' (fine), 'winzig' (tiny), or in compounds like 'Staubpartikel' (dust particle) or 'Russpartikel' (soot particle).
Feine Partikel in der Luft können die Gesundheit belasten.
Fine particles in the air can harm health.
particle
'das Teilchen' and 'die Partikel' can often mean the same thing: very small components of matter. In physics, people speak of 'Teilchen' or 'Partikeln', for example when talking about atoms or electrons. In linguistics, both words can also be used for short, invariable words like 'ja' or 'doch'. 'Teilchen' often sounds a bit simpler and more general in everyday language, while 'Partikel' sounds somewhat more technical. They are easy to confuse because in many contexts they really are very close in meaning. The most important thing is the context: dust, physics, or grammar.

Im Deutschkurs üben wir Partikeln wie „doch“ und „mal“.
In German class, we practice particles like 'doch' and 'mal'.
Im Sonnenlicht sieht man kleine Teilchen in der Luft.
In the sunlight, you can see small particles in the air.