ungewöhnlich
unusual
Deviating from the norm, the usual, or what is expected; strange, special, or remarkable.
Für April ist dieser plötzliche Schneefall sehr ungewöhnlich.
For April, this sudden snowfall is very unusual.

unusual
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unusual
Deviating from the norm, the usual, or what is expected; strange, special, or remarkable.
Für April ist dieser plötzliche Schneefall sehr ungewöhnlich.
For April, this sudden snowfall is very unusual.

The word is built simply: the prefix 'un-' is a negation, and 'gewöhnlich' means 'normal' or 'usual'. So 'ungewöhnlich' (unusual) literally means 'not usual'.
Es ist ungewöhnlich, im Mai noch Schnee zu haben.
It is unusual to still have snow in May.
'Ungewöhnlich' (unusual/unusually) can describe a noun (attributively/predicatively) or intensify another adjective or a verb (adverbially). In the second case, it means 'extraordinarily' or 'particularly'.
Er hat einen sehr ungewöhnlichen Beruf.
He has a very unusual job.
As an adverb, 'ungewöhnlich' (unusually) stands directly before the adjective or adverb it intensifies. It then expresses a high degree. Typical combinations are 'ungewöhnlich hoch' (unusually high), 'ungewöhnlich schnell' (unusually fast), or 'ungewöhnlich ruhig' (unusually quiet).
Die Preise für Benzin sind zurzeit ungewöhnlich hoch.
Gas prices are unusually high at the moment.
especially / special
'besonders' and 'ungewöhnlich' can both say that something is not completely normal or is noticeable. But 'besonders' is broader: it can highlight something positively as important, strong, or special. 'ungewöhnlich' puts more emphasis on something deviating from what is normal or expected. For that reason, 'ungewöhnlich' can also sound a little like 'strange', but it does not have to be negative. Learners may confuse the words because both fit with noticeable things. If you want to highlight something, often use 'besonders'. If you want to say that something is not usual, 'ungewöhnlich' fits better.

Es ist ungewöhnlich, dass er an einem Sonntag so früh im Büro ist.
It is unusual for him to be in the office so early on a Sunday.
Der Kuchen schmeckt heute besonders gut.
The cake tastes especially good today.