Toy I placed on top of list (4)
I believe the answer is:
lego
'toy' is the definition.
(I've seen this before)
'i placed on top of list' is the wordplay.
'i' becomes 'ego' (I've seen this before**).
'placed on' means one lot of letters go next to another.
'top of' says to take the initial letters.
The initial letter of 'list' is 'l'.
'ego' after 'l' is 'LEGO'.
(Other definitions for lego that I've seen before include "Kids' bricks" , "Toy building-bricks" , "Toy with interlocking blocks" , "Toy building bricks" , "constructed without care" .)