Thing of beauty initially on meeting (9)
I believe the answer is:
obsession
'thing' is the definition.
(thesaurus)
'of beauty initially on meeting' is the wordplay.
'initially' suggests taking the first letters.
'on' means one lot of letters go next to another.
'meeting' becomes 'session' (session is a kind of meeting**).
The initial letters of 'of beauty' is 'ob'.
'ob'+'session'='OBSESSION'
(Other definitions for obsession that I've seen before include "Compulsion, fixation" , "Fixed idea" , "Persistent preoccupation" , "Complex" , "Thing" .)