| usnic | <chemistry> Pertaining to, or designating, a complex acid obtained, as a yellow crystalline substance, from certain genera of lichens (Usnea, Parmelia, etc). Source: Websters Dictionary (01 Mar 1998) |
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| usnic acid | An organic acid extracted from the lichen Usnea barbata whichhas antibiotic properties, particularly against Gram-positive bacteriasuch at M. Tuberculosis as well as some pathogenic fungi. (09 Oct 1997) |