Understanding “About a Boy” (6)
I believe the answer is:
reason
'understanding' is the definition.
(I know that understanding can be written as reason)
'about a boy' is the wordplay.
'about' becomes 'rea' (I've seen this in other clues).
'a boy' becomes 'son' (synonyms).
'rea'+'son'='REASON'
(Other definitions for reason that I've seen before include "Sanity of senora" , "Capacity for rational thought" , "brain operations" , "Cause; think logically" , "Explanation or justification" .)