quarto vs 4to

quarto and 4to both are nouns.

Word	Noun	Adjective	Verb	Adverb
quarto	Yes	No	No	No
4to	Yes	No	No	No

As nouns, quarto and 4to are synonyms defined as:

quarto and 4to: the size of a book whose pages are made by folding a sheet of paper twice to form four leaves

quarto (noun)	4to (noun)
the size of a book whose pages are made by folding a sheet of paper twice to form four leaves	the size of a book whose pages are made by folding a sheet of paper twice to form four leaves