Muse partly under a toga (5)
I believe the answer is:
erato
'muse' is the definition.
(I know that Erato is a muse)
'partly under a toga' is the wordplay.
'partly' indicates the answer is hidden within the clue (part of the clue is used).
'ERATO' is hidden in the letters of 'under a toga'.
(Other definitions for erato that I've seen before include "Poet's inspiration" , "inspiration for poetry" , "daughter of Zeus" , "Muse of lyric love-poetry" , "Poetic Muse ; eighteen (anag.)" .)