Alan to shake, having no key (6)
I believe the answer is:
atonal
'having no key' is the definition.
(I've seen this in another clue)
'alan to shake' is the wordplay.
'shake' is an anagram indicator.
'alan'+'to'='alanto'
'alanto' with letters rearranged gives 'ATONAL'.
(Other definitions for atonal that I've seen before include "An alto (anag) - without a fixed key" , "Unaccented" , "Lacking traditional musical tone structure" , "Describes music not written in a particular key" , "As modernist works" .)