The Collaborative International Dictionary of English v.0.48:

Roccellic \Roc*cel"lic\, a. [F. roccellique, fr. roccelle
   archil, It. & NL. roccella, fr. It. rocca a rock, because
   archil grows on rock.] (Chem.)
   Pertaining to, or designating, a dibasic acid of the oxalic
   series found in archil (Roccella tinctoria, etc.), and
   other lichens, and extracted as a white crystalline substance
   C17H32O4.
   [1913 Webster]