Group of illustrious musicians? (4)
I believe the answer is:
trio
'group' is the definition.
(a group of three)
'of illustrious musicians?' is the wordplay.
'of' says the answer is hidden in the clue.
'TRIO' is hidden in the letters of 'illustrious musicians'.
(Other definitions for trio that I've seen before include "A group or set of three" , "wise men?" , "(Composition for) three performers" , "Group of three (musicians)" , "Band of three" .)