bridle vs keep back

bridle

verb
  • To check, restrain, or control with, or as if with, a bridle; as in bridle your tongue. 

  • To hold up one's head proudly or affectedly. 

  • To show hostility or resentment. 

  • To put a bridle on. 

noun
  • The headgear with which a horse is directed and which carries a bit and reins. 

  • A length of line or cable attached to two parts of something to spread the force of a pull, as the rigging on a kite for attaching line. 

  • A mooring hawser. 

  • A piece in the interior of a gunlock which holds in place the tumbler, sear, etc. 

  • A restraint; a curb; a check. 

  • A gesture expressing pride or vanity. 

keep back

verb
  • To restrict or restrain. 

  • To hold back; to refuse to give or share. 

  • To prevent (a pupil) from advancing in a course. 

  • To stay back; to refrain from approaching. 

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