Extremely simple harp designed for an angel (6)
I believe the answer is:
seraph
'angel' is the definition.
(seraph is a kind of angel)
'extremely simple harp designed for' is the wordplay.
'extremely' says to hollow out the word (remove centre letters) (only the extremes of the word are used).
'designed for' is an anagram indicator (letters re-designed).
'simple' with its middle removed is 'se'.
'harp' with letters rearranged gives 'raph'.
'se'+'raph'='SERAPH'
'an' is the link.
(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" .)