Lively song on piano almost complete (7)
I believe the answer is:
playful
'lively' is the definition.
(I've seen this before)
'song on piano almost complete' is the wordplay.
'song' becomes 'lay' (poetic term for a song).
'on' says to put letters next to each other.
'piano' becomes 'p' (musical abbreviation).
'almost' means to remove the last letter (almost the whole word is kept).
'complete' becomes 'full' (associated in meaning).
'full' with its last letter taken off is 'ful'.
'lay' put after 'p' is 'play'.
'play'+'ful'='PLAYFUL'
(Other definitions for playful that I've seen before include "Frisky" , "Teasing, unserious" , "In high spirits" , "Fun-loving" , "Full of fun" .)