hijab vs niqab

hijab

noun
  • A traditional headscarf worn by Muslim women, covering the hair and neck. 

  • The practice, among Muslim women, of covering the body after the age of puberty in front of non-related adult males. 

niqab

noun
  • A veil which covers the face, worn by some Muslim women as a part of sartorial hijab. 

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