der Regentropfen
raindrop
A single drop of water that falls from the sky as rain.
Ein großer Regentropfen landete genau auf meiner Nase.
A large raindrop landed right on my nose.

raindrop
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raindrop
A single drop of water that falls from the sky as rain.
Ein großer Regentropfen landete genau auf meiner Nase.
A large raindrop landed right on my nose.

The word is a clear compound of 'der Regen' (rain) and 'der Tropfen' (drop). It means exactly that literally: a drop of rain.
Der erste Regentropfen fiel auf die trockene Erde.
The first raindrop fell onto the dry ground.
Common adjectives are 'einzelne' (single), 'erste' (first), 'dicke' (large/heavy), or 'schwere' (heavy) raindrops. Typical verbs are 'fallen' (to fall) or 'prasseln' (to patter, when there are many).
Dicke Regentropfen prasselten gegen die Fensterscheibe.
Heavy raindrops pattered against the windowpane.
The singular 'der Regentropfen' (raindrop) is used to emphasize one single, isolated drop. The plural 'die Regentropfen' (raindrops) describes rain as a whole or a large number of drops.
Ein einziger Regentropfen kann der Anfang eines Gewitters sein.
A single raindrop can be the beginning of a thunderstorm.
rain
'der Regen' and 'der Regentropfen' both belong to weather and to water from clouds. 'der Regen' means the whole weather event or the amount of drops falling from the sky. 'der Regentropfen' means only one single drop. Learners may confuse the words because both have to do with rain. A practical rule: when talking about the weather, you usually use 'Regen'. When describing a single drop, 'Regentropfen' fits better.

Ein Regentropfen lief über das Fenster, während ich im Bus saß.
A raindrop ran down the window while I was sitting on the bus.
Wegen des starken Regens ist die Gruppe am Abend zu Hause geblieben.
Because of the heavy rain, the group stayed at home in the evening.