constraining vs imperative

constraining

noun
  • The act by which something is constrained. 

imperative

noun
  • An essential action, a must: something which is imperative. 

  • A verb in imperative mood. 

  • The grammatical mood expressing an order (see jussive). In English, the imperative form of a verb is the same as that of the bare infinitive. 

adj
  • Having semantics that incorporates mutable variables. 

  • Expressing a command; authoritatively or absolutely directive. 

  • Essential; crucial; extremely important. 

  • Of, or relating to the imperative mood. 

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