unzählig
countless
Describes such a large quantity of something that it cannot be counted or is very difficult to count; innumerable.
Am klaren Nachthimmel leuchteten unzählige Sterne.
Countless stars shone in the clear night sky.

countless
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countless
Describes such a large quantity of something that it cannot be counted or is very difficult to count; innumerable.
Am klaren Nachthimmel leuchteten unzählige Sterne.
Countless stars shone in the clear night sky.

The word is easy to understand if you analyze its parts: the prefix 'un-' means 'not', and the stem 'zähl' comes from the verb 'zählen' (to count). So 'unzählig' literally means 'not countable'.
Es gibt unzählige Wege, um nach Rom zu kommen.
There are countless ways to get to Rome.
'Unzählig' is often used to emphasize a large quantity. Common combinations are 'unzählige Male' (countless times), 'unzählige Menschen' (countless people), 'unzählige Möglichkeiten' (countless possibilities), or 'unzählige Beispiele' (countless examples).
Ich habe diesen Film schon unzählige Male gesehen.
I have seen this film countless times already.
'Unzählig' is an expressive word. It does not just mean 'many'; it emphasizes that the quantity is so large that it is overwhelming or impossible to grasp.
Auf der Demonstration versammelten sich unzählige Menschen.
Countless people gathered at the demonstration.
much / a lot
'viel' and 'unzählig' both describe a large amount. 'viel' is the normal and very general word. You use it in many everyday situations, even when the amount is simply large. 'unzählig' is stronger: it means that there are so many things that you can hardly count them, or cannot count them at all. It fits especially well with countable things in the plural, for example 'unzählige Fragen' (countless questions) or 'unzählige Sterne' (countless stars). 'viel' sounds more neutral, while 'unzählig' makes the amount seem especially large and often feels somewhat more vivid.

Am Strand lagen unzählige kleine Muscheln im Sand.
Countless small shells lay in the sand on the beach.
In der Stadt gibt es heute viel Verkehr.
There is a lot of traffic in the city today.