WordWeb Online

1. So thin as to transmit light
   "a hat with a cobwebby veil";
   - diaphanous, filmy, gauzy, gauze-like, gossamer, see-through, sheer, transparent, vaporous, vapourous [Brit, non-standard], vapory [US], vapoury [Brit, Cdn]
    
2. Covered with cobwebs
   "James was standing at the edge of a stack of boxes that towered up among the cobwebby rafters";
   - cobwebbed

See also: dirty, soiled, thin, unclean