The Collaborative International Dictionary of English v.0.48:
Arborous \Ar"bor*ous\, a. Formed by trees. [Obs.] [1913 Webster] From under shady, arborous roof. --Milton. [1913 Webster]WordNet (r) 3.0 (2006):
arborous adj 1: of or relating to or formed by trees; "an arborous roof" [syn: arborical, arboreal, arborary, arborous]