Being anonymous is indescribable (8)
I believe the answer is:
nameless
I believe this is a double definition.
'being anonymous' is the first definition.
('nameless' can be similar in meaning to 'anonymous')
'indescribable' is the second definition.
(thesaurus)
'is' acts as a link.
(Other definitions for nameless that I've seen before include "Difficult to describe" , "like the guy in the spaghetti movies?" , "not easily identified?" , "This undistinguished" , "Too unpleasant" .)