Time European is accepting border idea (5)
I believe the answer is:
theme
'idea' is the definition.
(I know that idea can be written as theme)
'time european is accepting border' is the wordplay.
'time' becomes 't' (abbreviation).
'european' becomes 'E' (abbreviation e.g. EU).
'is accepting' is an insertion indicator (inserted letters are accepted).
'border' becomes 'hem' (I've seen this before).
't'+'e'='te'
'te' placed around 'hem' is 'THEME'.
(Other definitions for theme that I've seen before include "Motif that's repeated" , "Motif, topic" , "subject,motif" , "tune used in Enigma Variations?" , "Thread, melody" .)