caste vs stratum

caste

noun
  • A separate and fixed order or class of persons in society who chiefly associate with each other. 

  • Hyponyms: Brahmin, Kshatriya, Shudra, Vaishya, varna 

  • Any of the hereditary social classes and subclasses of South Asian societies. 

  • A class of polymorphous eusocial insects of a particular size and function within a colony. 

stratum

noun
  • A class of society composed of people with similar social, cultural, or economic status. 

  • One of several parallel horizontal layers of material arranged one on top of another. 

  • A layer of sedimentary rock having approximately the same composition throughout. 

  • Any of the regions of the atmosphere, such as the stratosphere, that occur as layers. 

  • A layer of vegetation, usually of similar height. 

  • The level of accuracy of a computer's clock, relative to others on the network. 

  • A layer of tissue. 

How often have the words caste and stratum occurred in a corpus of books? (source: Google Ngram Viewer )