Wrong by a mile, effectively? (5)
I believe the answer is:
amiss
'wrong' is the definition.
(synonyms)
'by a mile effectively?' is the wordplay.
'by' says to put letters next to each other.
'mile effectively?' becomes 'miss' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'a' next to 'miss' is 'AMISS'.
Can you help me to learn more?
(Other definitions for amiss that I've seen before include "Not functioning properly" , "Unsuitable" , "Haywire" , "inappropriately" , "Fallacious" .)