Relative, respectable, imports ecstasy (5)
I believe the answer is:
niece
'relative' is the definition.
(type of relative)
'respectable imports ecstasy' is the wordplay.
'respectable' becomes 'nice' (similar in meaning).
'imports' means one lot of letters goes inside another (inserted letters are imported).
'ecstasy' becomes 'E' (informal term for the drug).
'nice' going around 'e' is 'NIECE'.
(Other definitions for niece that I've seen before include "Family relation" , "Family relative" , "Preparation for curdling milk" , "[PRIEST'S] daughter?" , "A sibling's child" .)