etlich
several
Indicates an indefinite but fairly large number of people or things; several, quite a few.
Bis das Projekt abgeschlossen war, vergingen noch etliche Monate.
Several more months passed before the project was completed.

several / quite a few
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several
Indicates an indefinite but fairly large number of people or things; several, quite a few.
Bis das Projekt abgeschlossen war, vergingen noch etliche Monate.
Several more months passed before the project was completed.

The word 'etlich' (several / quite a few) is used exclusively in the plural because it describes an indefinite quantity of multiple things or people. It is declined like a normal adjective before the noun.
Es gibt etliche Gründe für diese Entscheidung.
There are several reasons for this decision.
'Etlich' (several / quite a few) belongs more to written or more formal language. It is used less often in everyday conversation.
Der Autor hat zu diesem Thema etliche Bücher veröffentlicht.
The author has published several books on this topic.
'Etlich' (several / quite a few) is often used in connection with units of time or repetitions. Typical combinations are 'etliche Jahre' (several years), 'etliche Wochen' (several weeks), or 'etliche Male' (several times).
Ich habe diesen Film schon etliche Male gesehen.
I have seen this film several times already.
some / several
'einige' and 'etlich' both refer to an indefinite number. So you do not know exactly how many there are. 'einige' is very general and can mean a rather small to medium number. 'etlich' sounds stronger: it usually means quite a few, more than you might first expect. Also, 'etlich' feels a little less everyday than 'einige'. Learners may confuse the words because neither gives an exact number. If you want to stay neutral, 'einige' is usually safe. If you want to emphasize that there are quite a lot, 'etlich' fits better.

Am Wochenende löst Sofia etliche Aufgaben zur Vorbereitung auf den Test.
At the weekend, Sofia solves quite a few exercises to prepare for the test.
Im Park macht er einige Fotos von seiner Familie.
In the park, he takes some photos of his family.