jack-in-the-box vs plaything

jack-in-the-box and plaything both are nouns.

Word	Noun	Adjective	Verb	Adverb
jack-in-the-box	Yes	No	No	No
plaything	Yes	No	No	No

As nouns, plaything is a hypernym of jack-in-the-box; that is, plaything is a word with a broader meaning than jack-in-the-box:

jack-in-the-box: plaything consisting of a toy clown that jumps out of a box when the lid is opened
plaything: an artifact designed to be played with

Other hypernyms of jack-in-the-box include toy.

jack-in-the-box (noun)	plaything (noun)
plaything consisting of a toy clown that jumps out of a box when the lid is opened	an artifact designed to be played with