Toy weapon on edge of seat (6)
I believe the answer is:
trifle
'toy' is the definition.
(both can mean to play with)
'weapon on edge of seat' is the wordplay.
'weapon' becomes 'rifle' (rifle is a kind of weapon).
'on' says to put letters next to each other.
'edge of seat' becomes 't' (I can't justify this - if you can you should give a lot more credence to this answer).
'rifle' put after 't' is 'TRIFLE'.
(Other definitions for trifle that I've seen before include "Type of dessert" , "A little thing for the pudding" , "Dessert - toy" , "that doesn't matter" , "Small beer" .)