A half rum can be injurious (7)
I believe the answer is:
harmful
'injurious' is the definition.
(similar in meaning)
'a half rum can be' is the wordplay.
'can be' is an anagram indicator.
'half'+'rum'='halfrum'
'halfrum' is an anagram of 'HARMFUL'.
(Other definitions for harmful that I've seen before include "Dangerous, damaging" , "Causing injury or damage, say poison or malice" , "Deleterious" , "Half rum (anag.)" , "Injurious" .)