fettered vs under lock and key

fettered

adj
  • Of the feet: bent backward and apparently unfit for walking. 

  • Bound by chains or shackles. 

  • Restricted. 

under lock and key

prep
  • imprisoned with little or no chance of escape; locked up. 

  • safely guarded; locked away. 

How often have the words fettered and under lock and key occurred in a corpus of books? (source: Google Ngram Viewer )