Second lyre is out of tune (5)
I believe the answer is:
sharp
'out of tune' is the definition.
(I've seen this in another clue)
'second lyre' is the wordplay.
'second' becomes 's' (common abbreviation).
'lyre' becomes 'harp' (I've seen this before).
's'+'harp'='SHARP'
'is' acts as a link.
(Other definitions for sharp that I've seen before include "music feature" , "Incisive" , "Unscrupulous character" , "Cutting; acidic" , "Acidic; pointed" .)