Relative up in EC excited at first (5)
I believe the answer is:
niece
'relative' is the definition.
(type of relative)
'up in ec excited at first' is the wordplay.
'up' is a reversal indicator (in down clue: letters go upwards).
'at first' says to take the initial letters.
The first letter of 'excited' is 'e'.
'in' backwards is 'ni'.
'ni'+'ec'+'e'='NIECE'
(Other definitions for niece that I've seen before include "A younger female relative" , "Family relation" , "Son's cousin" , "Female relation" , "One of the family" .)