Words of wisdom always in serenade (6)
I believe the answer is:
saying
'words of wisdom' is the definition.
(I've seen this in another clue)
'always in serenade' is the wordplay.
'always' becomes 'ay' (archaic term for 'always').
'in' means one lot of letters goes inside another.
'serenade' becomes 'sing' (to serenade someone is to sing to them).
'ay' inserted inside 'sing' is 'SAYING'.
(Other definitions for saying that I've seen before include "Uttering" , "Gnome" , "Adage, maxim" , "Epigram" , "Motto" .)