zweifelsohne
undoubtedly
Expresses that something is certain and indisputable; without any doubt.
Sie ist zweifelsohne die beste Kandidatin für diesen Job.
She is undoubtedly the best candidate for this job.

undoubtedly
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undoubtedly
Expresses that something is certain and indisputable; without any doubt.
Sie ist zweifelsohne die beste Kandidatin für diesen Job.
She is undoubtedly the best candidate for this job.

The word is made up of 'Zweifel' (doubt) and 'ohne' (without). So it literally means 'ohne Zweifel' (without a doubt), which makes it easy to understand and remember.
Das ist zweifelsohne die richtige Entscheidung.
That is undoubtedly the right decision.
As an adverb, 'zweifelsohne' (undoubtedly) can stand in different positions in the sentence. If it is in position 1, the conjugated verb follows immediately. But it can also stand after the verb and the subject.
Zweifelsohne hat er sein Bestes gegeben.
Undoubtedly, he gave it his best.
'Zweifelsohne' (undoubtedly) belongs more to written language or to a formal, elevated style. It is used less often in everyday colloquial speech.
Die Ergebnisse der Studie sind zweifelsohne von großer Bedeutung.
The results of the study are undoubtedly of great importance.
certain / specific
'bestimmt' and 'zweifelsohne' can both express that you consider something certain. 'bestimmt' is very natural in everyday language and can also express a strong assumption. 'zweifelsohne' sounds stronger and somewhat more formal: it means that there really is no doubt. Learners may confuse the words because both show certainty. In conversations, people usually say 'bestimmt'. In a presentation, text, or clear assessment, 'zweifelsohne' often fits better.

Diese Entscheidung ist zweifelsohne wichtig für die Zukunft der Firma.
This decision is undoubtedly important for the future of the company.
Herr Demir kommt bestimmt am Montag zum Bewerbungsgespräch.
Mr. Demir will certainly come to the job interview on Monday.