Russian doll

Russian doll (plural Russian dolls)

1. One of a set of hollow nesting dolls, usually wooden and decorated.
   • 2014, Fiona McArthur, Midwife's Mistletoe Baby, Harlequin (→ISBN), page 97:

     When she opened it he saw her eyes flash to Simon's, saw the tremulous smile and the stroke of her finger down the painted face of the Russian doll. Those dolls that had other dolls inside.

2. (figuratively) An issue or situation which repeatedly reveals more levels of complexity.
   • 2012, G. Bernard, Principia Economica, Springer Science & Business Media (→ISBN), page 2:

     Any society is thus like a Russian doll, only much more complicated than this toy, whose inclusions are linear, i.e. unidimensional. A society can be imagined as a multidimensional Russian doll.

   • 2014, Julie Armstrong, Experimental Fiction: An Introduction for Readers and Writers, Bloomsbury Publishing (→ISBN), page 173:

     The History of Love by Nicole Krauss has been described as a complex Russian-doll structure; a narrative inside another inside another. The form is fragmented. There are multiple voices, multiple narrative strands set out […]

   • 2015, David d'Avray, Papacy, Monarchy and Marriage 860–1600, Cambridge University Press (→ISBN), page 128:

     Like a Russian doll, a document within the document within the document follows. This last document is in fact the last part of the document discussed in the previous section: the résumé of the evidence and the verdict.

• (wooden doll): matryoshka, matreshka, matrëshka, matrioshka, matrioshka doll, matryoshka doll, babushka
• (both senses): nesting doll

• Matryoshka doll on Wikipedia.Wikipedia
• “Russian doll” (US) / “Russian doll” (UK) in Oxford Dictionaries, Oxford University Press.