ungemein
extremely
To a very high degree; extraordinarily, extremely. Used as an intensifying adverb.
Die Wanderung war ungemein anstrengend, aber die Aussicht hat sich gelohnt.
The hike was extremely strenuous, but the view was worth it.

extremely
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extremely
To a very high degree; extraordinarily, extremely. Used as an intensifying adverb.
Die Wanderung war ungemein anstrengend, aber die Aussicht hat sich gelohnt.
The hike was extremely strenuous, but the view was worth it.

The word consists of the prefix 'un-' and the adjective 'gemein', which here means 'ordinary'. So 'ungemein' literally means 'unusual' and is used as an intensifier in the sense of 'extraordinarily' or 'extremely'.
Das Konzert war ein ungemein beeindruckendes Erlebnis.
The concert was an extremely impressive experience.
'Ungemein' is used almost exclusively as an adverb to intensify adjectives or other adverbs. It stands directly before the word it intensifies. It is not used as a standalone predicate adjective.
Diese Aufgabe ist ungemein schwierig zu lösen.
This task is extremely difficult to solve.
'Ungemein' belongs more to elevated written language or a more formal style. In everyday colloquial speech, other intensifiers such as 'sehr' (very), 'total' (totally), or 'echt' (really) are often preferred.
Die Autorin verfügt über ein ungemein breites Wissen.
The author has an extremely broad knowledge.
very
'sehr' and 'ungemein' both intensify a quality or statement. 'sehr' is neutral, simple, and natural in almost every context. 'ungemein' also means 'very', but it sounds stronger and somewhat more elevated or emphatic. It is often used when you want to highlight something as especially great, helpful, important, or interesting. In everyday language, 'sehr' is usually the safe choice; 'ungemein' feels more expressive.

Der kurze Tipp war für die Prüfung ungemein hilfreich.
The short tip was extremely helpful for the exam.
Nach der Arbeit ist die Verkäuferin sehr freundlich geblieben.
After work, the saleswoman remained very friendly.