unabsichtlich
unintentionally
Describes an action that happens without intention or deliberate purpose; by accident.
Ich habe die Vase unabsichtlich umgestoßen.
I unintentionally knocked over the vase.

unintentionally
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unintentionally
Describes an action that happens without intention or deliberate purpose; by accident.
Ich habe die Vase unabsichtlich umgestoßen.
I unintentionally knocked over the vase.

The word is structured simply: the prefix 'un-' negates the word 'absichtlich' (intentionally). 'Absichtlich' in turn comes from the noun 'die Absicht' (intention). So 'unabsichtlich' (unintentionally) literally means 'without intention.'
Entschuldigung, ich habe Sie unabsichtlich angerempelt.
Sorry, I bumped into you unintentionally.
As an adverb, 'unabsichtlich' (unintentionally) describes how an action happens. It usually comes after the conjugated verb and any objects.
Er hat die Datei unabsichtlich gelöscht.
He unintentionally deleted the file.
This word is very often used to apologize for a mistake or to explain that a negative action was an accident. It reduces one's own blame.
Ich habe dir unabsichtlich wehgetan, das tut mir sehr leid.
I unintentionally hurt you; I'm very sorry.
conscious / deliberate
'bewusst' and 'unabsichtlich' are opposites when it comes to the intention behind an action. 'bewusst' means: someone does something deliberately and knows what they are doing. 'unabsichtlich' means: something happens by mistake, without a plan or intention. If you want to say that someone acted responsibly and deliberately, 'bewusst' fits. If something was only a mistake or a coincidence, 'unabsichtlich' fits.

Im Gespräch hat Maria unabsichtlich den falschen Namen gesagt.
During the conversation, Maria unintentionally said the wrong name.
Er hat bewusst einen früheren Zug genommen, um pünktlich zu sein.
He deliberately took an earlier train to be on time.