railbed vs underlay

railbed

noun
  • The substructure of a railway, underlying the tracks; the roadbed of a railroad. 

underlay

noun
  • A layer (of earth, etc.) that lies under another; substratum. 

  • A piece of paper pasted under woodcuts, stereotype plates, etc. in a form, to bring them up to the necessary level for printing. 

  • Lyrics; or more specifically, the way in which lyrics are assigned to musical notes. 

  • Anything that is underlaid. 

  • A soft floor covering that lies under a carpet. 

verb
  • To lay (something) underneath something else; to put under. 

  • To put a tap on (a shoe). 

  • simple past tense of underlie 

  • To provide a support for something; to raise or support by something laid under. 

  • To incline from the vertical. 

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