Regularly play free instrument (4)
I believe the answer is:
lyre
'instrument' is the definition.
(lyre is a kind of instrument)
'regularly play free' is the wordplay.
'regularly' means one should take alternating letters (regularly take one letter, leave next etc.).
'play'+'free'='playfree'
The alternate letters of 'playfree' are 'LYRE'.
(Other definitions for lyre that I've seen before include "Ancient Greek harp" , "Rely (anag.)" , "Harp used by ancient Greeks" , "Music-maker" , "Ancient Greece harp" .)