Punishing Oscar for being easily frightened without Victor (7)

I believe the answer is:

onerous

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'punishing' is the definition.
(thesaurus)

I can't explain the remainder of the clue.

(Other definitions for onerous that I've seen before include "Burdensome, heavy kind of duty" , "Involving much work" , "Heavy, difficult to do or bear" , "Effortful" , "'Heavy, burdensome (7)'" .)

I've seen this clue in the Irish Times.

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