Article inspiring enthusiasm outwardly in subject (5)
I believe the answer is:
theme
'subject' is the definition.
(theme can mean a topic or subject)
'article inspiring enthusiasm outwardly' is the wordplay.
'article' becomes 'the' (the definite article in English).
'inspiring' indicates putting letters inside.
'outwardly' means to remove the middle letters (only the outermost letters are used).
'enthusiasm' with its centre removed is 'em'.
'the' enclosing 'em' is 'THEME'.
'in' is the link.
(Other definitions for theme that I've seen before include "Subject (on which person writes, speaks)" , "Topic; melody" , "[(type of) PARK]" , "subject,motif" , "thing under discussion" .)