Second best? That's a laugh (6)
I believe the answer is:
scream
'that's a laugh' is the definition.
(scream is a kind of laugh)
'second best?' is the wordplay.
'second' becomes 's' (common abbreviation).
'best?' becomes 'cream' (both can mean the elite).
's'+'cream'='SCREAM'
(Other definitions for scream that I've seen before include "noise?" , "Sound terrified" , "Hilarious character" , "A shrill cry of fright" , "Make high shrill sound as from fear" .)