Satirical drawing showing face of Onassis on board container (7)
I believe the answer is:
cartoon
'satirical drawing' is the definition.
(I've seen this before)
'face of onassis on board container' is the wordplay.
'face of' suggests taking the first letters.
'on board' means one lot of letters goes inside another.
'container' becomes 'carton' (carton is a kind of container).
The initial letter of 'onassis' is 'o'.
'o' put inside 'carton' is 'CARTOON'.
'showing' is the link.
(Other definitions for cartoon that I've seen before include "Witty drawing" , "Humorous or satirical drawing" , "eg 'The Simpsons'" , "Comic drawing" , "could make one laugh" .)