mood ringn. a ring set with a stone containing heat-sensitive crystals which change colour according to body temperature, supposed in this way to reflect the wearer's mood.
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1975 New Scientist 30 Oct. 298/2 The Mood Ring—a finger ornament which changes colour with the wearer's emotions.
1995 Denver Post 16 Jan. e3/1 The younger baby boomers, whose cultural touchstones included disco, divorce, mood rings and ‘The Brady Bunch’.