Hogshead is as much as one can hold - otherwise, it could be dangerous (7)

I believe the answer is:

harmful

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'be dangerous' is the definition.
(similar in meaning)

I don't understand the remainder of the clue.

(Other definitions for harmful that I've seen before include "Causing injury or damage, say poison or malice" , "Injurious" , "Deleterious" , "Dangerous, damaging" , "Noxious" .)

I've seen this clue in The Irish Times.

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