Extremely simple harp designed for an angel (6)
I believe the answer is:
seraph
'for an angel' is the definition.
(seraph is a kind of angel)
'extremely simple harp designed' is the wordplay.
'extremely' says to hollow out the word (remove centre letters) (only the extremes of the word are used).
'designed' indicates an anagram (designed with the letters).
'simple' with its centre removed is 'se'.
'harp' with letters rearranged gives 'raph'.
'se'+'raph'='SERAPH'
(Other definitions for seraph that I've seen before include "Angel with winged head of child" , "Angelic type" , "He raps the heavenly being wrongly" , "Turn of phase for an angel" , "Heavenly creature" .)