gossamer vs cobwebby

gossamer is a noun but cobwebby is not a noun.

Word	Noun	Adjective	Verb	Adverb
gossamer	Yes	Yes	No	No
cobwebby	No	Yes	No	No

As adjectives, gossamer and cobwebby are synonyms defined as:

Other synonyms of gossamer include diaphanous, filmy, gauze-like, gauzy, see-through, sheer, transparent, vaporous, vapourous.

gossamer (noun)	cobwebby (noun)
a gauze fabric with an extremely fine texture
filaments from a web that was spun by a spider

gossamer (adjective)	cobwebby (adjective)
characterized by unusual lightness and delicacy	covered with cobwebs
so thin as to transmit light	so thin as to transmit light