Chem. Also -ine. [f. USN-EA + -IN1.] Usnic acid.
1861. H. Macmillan, Footn. fr. Page Nat., 82. Alpine lichens generally are more or less of a brown or black colour. This peculiarity seems to be owing to the presence of usnine or usnic acid.
1867. Brande & Cox, Dict. Sci., etc., III. 912/2. Usnin or Usnic Acid … forms yellow crystals, which with great difficulty are fused like a resin.
