Pleasant having European relation (5)
I believe the answer is:
niece
'relation' is the definition.
(I know that relation can be written as niece)
'pleasant having european' is the wordplay.
'pleasant' becomes 'nice' (similar in meaning).
'having' means one lot of letters goes inside another.
'european' becomes 'e' (abbreviation e.g. EU).
'nice' enclosing 'e' is 'NIECE'.
(Other definitions for niece that I've seen before include "Family relative" , "Kinswoman" , "Son's cousin" , "member of different generation" , "Brother's girl" .)