guardrail vs parapet

guardrail

noun
  • A rail set alongside a dangerous place as a barrier, to improve safety. 

  • Any barrier designed to prevent accidents or mistakes. 

parapet

noun
  • A low protective wall. 

  • A fortification consisting of a wall. 

  • Part of a perimeter that extends above the roof. 

  • Hyponym: balustrade 

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