Obscurely see a form that's terrifying (8)
I believe the answer is:
fearsome
'terrifying' is the definition.
(thesaurus)
'obscurely see a form' is the wordplay.
'obscurely' indicates an anagram.
'see'+'a'+'form'='seeaform'
'seeaform' anagrammed gives 'FEARSOME'.
'that's' acts as a link.
(Other definitions for fearsome that I've seen before include "Fame rose and became frightening" , "Awful" , "Of frightening appearance" , "Frightful" , "Horrendous" .)