Herb's terrible anger, wearing glasses (7)
I believe the answer is:
oregano
'herb's' is the definition.
(oregano is a kind of herb)
'terrible anger wearing glasses' is the wordplay.
'terrible' indicates anagramming the letters.
'wearing' means one lot of letters goes inside another.
'glasses' becomes 'oo' (OO looks like spectacles).
'anger' with letters rearranged gives 'regan'.
'regan' put into 'oo' is 'OREGANO'.
(Other definitions for oregano that I've seen before include "herbal preparation" , "Pizza herb" , "aromatic plant" , "Gear Ono up for the herb" , "Wild marjoram" .)