acorn vs oak tree

acorn

noun
  • The fruit of the oak, being an oval nut growing in a woody cup or cupule. 

  • A cone-shaped piece of wood on the point of the spindle above the vane, on the mast-head. 

  • See acorn-shell. 

  • A testicle. 

oak tree

noun
  • A tree of the genus Quercus, bearing acorns and having lobed leaves. 

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