Smooth kid, maybe summoned to court lassie ultimately (5)
I believe the answer is:
suede
'smooth kid maybe' is the definition.
(kid is a type of leather)
'summoned to court lassie ultimately' is the wordplay.
'summoned to court' becomes 'sued'.
'ultimately' suggests the final letters.
The final letter of 'lassie' is 'e'.
'sued'+'e'='SUEDE'
(Other definitions for suede that I've seen before include "Soft goatskin" , "Brushed leather" , "Form of leather" , "Fabric" , "material used in gloves" .)