The phrase 'not spare the rod' is an idiom that means to punish someone for their misdeeds. The crossword solutions for this phrase are SPANK (5 letters), DOWSE (5 letters), and SNAPTHEWHIP (11 letters). SPANK is a verb meaning to hit someone as a form of punishment, DOWSE is a verb meaning to hit someone with a stick or rod, and SNAPTHEWHIP is an idiom meaning to punish someone severely. All three words refer to punishing someone for their misdeeds, which is the meaning of the phrase 'not spare the rod'.