One living alone before being joined by small child (7)
I believe the answer is:
eremite
'one living alone' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'before being joined by small child' is the wordplay.
'before' becomes 'ere' (poetic term for 'before').
'being joined by' says to put letters next to each other.
'small child' becomes 'mite' (informal term).
'ere'+'mite'='EREMITE'
Can you help me to learn more?
(Other definitions for eremite that I've seen before include "Christian hermit or recluse" , "Solitary" , "Religious person" , "ascetic" , "Christian living in severe circumstances" .)