From Latin folium (leaf). Doublet of foil and folio.


folium (countable and uncountable, plural foliums or folia)

  1. A leaf, especially a thin leaf or plate.
  2. (geometry) A curve of the third order, consisting of two infinite branches having a common asymptote. The curve has a double point, and a leaf-shaped loop.
  3. (uncountable) Synonym of turnsole (purple dye)

Part or all of this entry has been imported from the 1913 edition of Webster’s Dictionary, which is now free of copyright and hence in the public domain. The imported definitions may be significantly out of date, and any more recent senses may be completely missing.
(See the entry for folium in
Webster’s Revised Unabridged Dictionary, G. & C. Merriam, 1913.)



From Proto-Indo-European *bʰolh₃yom (leaf), from *bʰleh₃- (blossom, flower). Alternatively from *dʰolyom (*dʰelh₁- (be green)), whence Welsh dail and Middle Irish duille.



folium n (genitive foliī or folī); second declension

  1. a leaf
  2. a petal
  3. a sheet or leaf of paper
  4. (figuratively) trifle, thing of no consequence


Second-declension noun (neuter).

Case Singular Plural
Nominative folium folia
Genitive foliī
Dative foliō foliīs
Accusative folium folia
Ablative foliō foliīs
Vocative folium folia

1Found in older Latin (until the Augustan Age).

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  • fŏlĭum in Charlton T. Lewis and Charles Short (1879) A Latin Dictionary, Oxford: Clarendon Press
  • folium in Charlton T. Lewis (1891) An Elementary Latin Dictionary, New York: Harper & Brothers
  • folium in Charles du Fresne du Cange’s Glossarium Mediæ et Infimæ Latinitatis (augmented edition with additions by D. P. Carpenterius, Adelungius and others, edited by Léopold Favre, 1883–1887)
  • fŏlĭum in Gaffiot, Félix (1934) Dictionnaire illustré Latin-Français, Hachette, page 678/1
  • folium” on page 719/3 of the Oxford Latin Dictionary (1st ed., 1968–82)
  • Niermeyer, Jan Frederik (1976), “folium”, in Mediae Latinitatis Lexicon Minus, Leiden, Boston: Brill, page 439/2