Somehow creep into party (9)
I believe the answer is:
reception
'party' is the definition.
(reception is a kind of party)
'somehow creep into' is the wordplay.
'somehow' indicates anagramming the letters.
'creep'+'into'='creepinto'
'creepinto' is an anagram of 'RECEPTION'.
(Other definitions for reception that I've seen before include "at home" , "How one is greeted" , "drinks party" , "Formal function" , "A social event" .)