Communication left by one with a boy, about 1 (7)
I believe the answer is:
liaison
'communication left' is the definition.
Although both the answer and definition are singular nouns, I cannot understand how they can define each other.
'one with a boy about 1' is the wordplay.
'one with a' becomes 'lia' (I can't explain this - if you can you should give a lot more credence to this answer).
'boy' becomes 'son' (synonyms).
'about' is a charade indicator (letters next to each other).
'l' becomes 'I' (Roman numeral).
'son' after 'i' is 'ison'.
'lia'+'ison'='LIAISON'
'by' acts as a link.
Can you help me to learn more?
(Other definitions for liaison that I've seen before include "Illicit romance" , "Secret love affair" , "sexual adventure" , "Mil. coordination; illicit affair" , "Channel of communication" .)