Impatience ultimately seen in pleasant relative (5)
I believe the answer is:
niece
'relative' is the definition.
(type of relative)
'impatience ultimately seen in pleasant' is the wordplay.
'ultimately' says to take the final letters.
'seen in' is an insertion indicator.
'pleasant' becomes 'nice' (associated in meaning).
The last letter of 'impatience' is 'e'.
'e' going into 'nice' is 'NIECE'.
(Other definitions for niece that I've seen before include "Female family member" , "A sibling's daughter" , "Female relation" , "girl further down the line" , "Brother's daughter" .)