Likewise, one left in this manner (4)
I believe the answer is:
also
'likewise' is the definition.
(synonyms)
'one left in this manner' is the wordplay.
'one left' becomes 'al' (I've seen this in other clues).
'in this manner' becomes 'so' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'al'+'so'='ALSO'
Can you help me to learn more?
(Other definitions for also that I've seen before include "As well, in addition" , "an indication of more to come" , "into the bargain" , "on top" , "To boot" .)