
regnen
to rain
The falling of water droplets from the clouds. The verb is usually used impersonally with 'es' (it).
Wenn es morgen nicht regnet, machen wir einen Ausflug.
If it doesn't rain tomorrow, we'll go on a trip.
to rain
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to rain
The falling of water droplets from the clouds. The verb is usually used impersonally with 'es' (it).
Wenn es morgen nicht regnet, machen wir einen Ausflug.
If it doesn't rain tomorrow, we'll go on a trip.

to rain down
Used figuratively for the falling or arrival of a large amount of something.
Nach der Ankündigung regnete es Kritik von allen Seiten.
After the announcement, criticism rained down from all sides.
The verb 'regnen' (to rain) is the action that leads to the noun 'der Regen' (rain). When it rains, rain falls from the sky.
Wegen des starken Regens mussten wir drinnen bleiben.
Because of the heavy rain, we had to stay indoors.
In its literal meaning, 'regnen' (to rain) is an impersonal verb. It is almost always used with the formal subject 'es' (it). You say 'Es regnet' (It is raining), not 'Der Himmel regnet' (The sky is raining).
Gestern hat es den ganzen Tag geregnet.
Yesterday it rained all day.
To describe the intensity of the rain, you can use adverbs. Common combinations are 'stark regnen' (to rain heavily), 'leicht regnen' (to rain lightly), or the idiom 'in Strömen regnen' (to pour with rain).
Als wir aus dem Kino kamen, regnete es in Strömen.
When we came out of the cinema, it was pouring with rain.
In the figurative sense, no water falls; instead, a large amount of something else comes in. The context makes this clear, for example when criticism, prizes, or compliments 'regnet' (rain down).
Nach seinem Sieg regnete es Glückwünsche von allen Seiten.
After his victory, congratulations rained down from all sides.
to pee / to drizzle
Both words can describe light rain. “Regnen” is the neutral and generally appropriate term, whereas “pinkeln” sounds crude and colloquial in this figurative sense. Use “regnen” in a normal weather description; “pinkeln” is more likely to be heard jokingly or in very casual conversation.

Heute regnet es nur leicht, deshalb nehmen wir keinen Regenschirm mit.
It's only raining lightly today, so we're not taking an umbrella.
Mein Nachbar sagt scherzhaft, dass es heute nur ein bisschen pinkelt.
My neighbor jokes that it's only peeing a little today.