Discovers a wife's plaything (6)
I believe the answer is:
seesaw
'plaything' is the definition.
(seesaw is a kind of plaything)
'discovers a wife's' is the wordplay.
'discovers' becomes 'sees' ('see' can be a synonym of 'discover').
'wife' becomes 'w'.
'sees'+'a'+'w'='SEESAW'
(Other definitions for seesaw that I've seen before include "Rock unsteadily" , "youngsters' game" , "Playground furniture" , "Playground equipment for kids" , "Up-and-down children's game with plank on barrel" .)