undergarment vs undies

undergarment

noun
  • Any garment worn underneath others, especially one worn next to the skin; an item of underwear. 

  • Temple garments worn by the followers of the Church of Jesus Christ of Latter-day Saints. 

undies

noun
  • underwear, underpants 

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