Abroad, one loved touring northern plain (9)
I believe the answer is:
unadorned
'plain' is the definition.
('unadorned' can be similar in meaning to 'plain')
'abroad one loved touring northern' is the wordplay.
'abroad one' becomes 'un' (French for 'one' - when abroad).
'loved' becomes 'adored' ('adored' can be similar in meaning to 'loved').
'touring' means one lot of letters goes inside another (touring can mean going round).
'northern' becomes 'n' (abbreviation e.g. N. Ireland).
'adored' enclosing 'n' is 'adorned'.
'un'+'adorned'='UNADORNED'
(Other definitions for unadorned that I've seen before include "Not decorated, plain and simple" , "Without embellishment" , "Plain, undecorated" , "Simple and plain as around den" .)