Likely – to be responsible (6)
I believe the answer is:
liable
This clue is a double definition.
'likely' is the first definition.
(similar in meaning)
'to be responsible' is the second definition.
('liable' can be similar in meaning to 'responsible')
(Other definitions for liable that I've seen before include "Legally obligated" , "Likely" , "legally obliged, held responsible" , "Apt to" , "'Responsible, answerable (6)'" .)