Consider a topiarist to have a muse (5)
I believe the answer is:
erato
'a muse' is the definition.
(I know that Erato is a muse)
'consider a topiarist to have' is the wordplay.
'to have' says the answer is hidden in the clue.
'ERATO' is hidden within 'consider a topiarist'.
(Other definitions for erato that I've seen before include "Inspiring female" , "daughter of Zeus" , "One of the Muses" , "Muse of lyric love-poetry" , "goddess" .)