Powerless or defenceless (8)
I believe the answer is:
helpless
I believe this is a double definition.
'powerless' is the first definition.
(similar in meaning)
'defenceless' is the second definition.
(synonyms)
(Other definitions for helpless that I've seen before include "Unable to cope, without resources" , "Unable to manage independently" , "Unable to defend oneself" , "Powerless, defenceless" , "Uncontrollable (with laughter)" .)