Solitary type referring to sign welcoming son (7)
I believe the answer is:
recluse
'solitary' is the definition.
(thesaurus)
'referring to sign welcoming son' is the wordplay.
'referring to' becomes 're'.
'sign' becomes 'clue' (clue is a kind of sign**).
'welcoming' means one lot of letters goes inside another (in sense of 'inviting in').
'son' becomes 's'.
'clue' enclosing 's' is 'cluse'.
're'+'cluse'='RECLUSE'
'type' is the link.
I am not very happy about this link. It may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for recluse that I've seen before include "Person living in solitude" , "What, say, Howard Hughes became" , "company leaver" , "A loner, one who keeps to himself" , "One who avoids others" .)