As one outside home, very unlike welcome guest (9)
I believe the answer is:
uninvited
'unlike welcome guest' is the definition.
'as one outside home very' is the wordplay.
'as one' becomes 'united' (I've seen this before).
'outside' indicates putting letters inside.
'home' becomes 'in' ('he's home' can mean 'he's in').
'very' becomes 'v' (abbreviation).
'in'+'v'='inv'
'united' enclosing 'inv' is 'UNINVITED'.
(Other definitions for uninvited that I've seen before include "not wanted" , "Gatecrasher" , "Intruder" .)