adult toy vs plaything

adult toy and plaything both are nouns.

Word	Noun	Adjective	Verb	Adverb
adult toy	Yes	No	No	No
plaything	Yes	No	No	No

As nouns, plaything is a hypernym of adult toy; that is, plaything is a word with a broader meaning than adult toy:

adult toy: A sex toy is an object or device that is primarily used to facilitate human sexual pleasure, such as a dildo or vibrator.
plaything: an artifact designed to be played with

Other hypernyms of adult toy include toy.

adult toy (noun)	plaything (noun)
A sex toy is an object or device that is primarily used to facilitate human sexual pleasure, such as a dildo or vibrator.	an artifact designed to be played with