Second-best shriek (6)
I believe the answer is:
scream
'shriek' is the definition.
(I know that shriek is a more specific form of the action scream)
'second-best' is the wordplay.
'second' becomes 's' (common abbreviation).
'best' becomes 'cream' (as in 'the cream of the crop').
's'+'cream'='SCREAM'
(Other definitions for scream that I've seen before include "Hoot - yell in pain" , "Cry of anguish" , "Loud piercing cry" , "A shrill cry of fright" , "Yell for creams" .)