adverb
without incident; uneventfully; safely
Adverbial use meaning that something proceeds without trouble, accident, or notable events. Often used with verbs of movement or completion.
長い旅だったが、ことなく目的地に着いた。
It was a long journey, but we arrived at our destination without incident.
手術はことなく終わった。
The surgery ended uneventfully.
suffix
without doing ...; without ...
Suffix-like use attaching to the dictionary form of a verb to mean 'without doing that action'. Equivalent to ～ないで or ～ずに, but more literary and formal.
彼は休むことなく働き続けた。
He kept working without resting.
諦めることなく挑戦しなさい。
Keep trying without giving up.
無事に is a common adverb meaning 'safely' or 'without incident', similar to sense 1 of ことなく, but ことなく is more literary and less common in everyday speech.
～ずに is a negative verb suffix meaning 'without doing', similar to sense 2 of ことなく, but ずに is more common in modern Japanese, while ことなく is more formal and often found in written language.
Derived from the noun 事 (こと, 'thing, matter') + the adverbial form of the negative adjective 無い (ない, 'not exist'). Literally 'without a thing (happening)', it grammaticalized into a suffix meaning 'without doing'.