seashell vs univalve

seashell

noun
  • The empty shell of a marine mollusk. 

  • A very light pink colour, like that of some seashells. 

adj
  • Of a very light pink colour, like that of some seashell. 

univalve

noun
  • A univalve mollusk or its shell. 

adj
  • having one valve; typically used to refer to mollusks, notably slugs and snails. 

  • consisting of a single valve or piece, used to refer to a shell. 

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