Insect, as customer squashed by King George (11)
I believe the answer is:
grasshopper
'insect' is the definition.
(grasshopper is a kind of insect)
'as customer squashed by king george' is the wordplay.
'customer' becomes 'shopper' (shopper is a kind of customer).
'squashed by' means one lot of letters go next to another.
'king george' becomes 'gr' (Georgius Rex).
'as'+'shopper'='asshopper'
'asshopper' after 'gr' is 'GRASSHOPPER'.
(Other definitions for grasshopper that I've seen before include "Jumping insect" , "Excellent jumper" , "Type of cricket" , "Insect (that won't stay still for long?)" , "Chirping insect" .)