feeble vs insubstantial

feeble

adj
  • Lacking force, vigor, or effectiveness in action or expression; faint. 

  • Deficient in physical strength. 

insubstantial

adj
  • Lacking substance; not real or strong. 

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