Commentator's dread for earth (5)
I believe the answer is:
terra
'earth' is the definition.
(thesaurus)
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for terra that I've seen before include "Dry land" , "Land (Latin)" , "Centre" , "Legally land" , "-- Firma; -- incognita" .)