Moth ultimately ensnared by dreadful trapdoor spider? (9)
I believe the answer is:
arthropod
'spider?' is the definition.
(spider is a kind of arthropod)
'moth ultimately ensnared by dreadful trapdoor' is the wordplay.
'ultimately' suggests the final letters.
'ensnared by' means one lot of letters goes inside another (I've seen this in other clues).
'dreadful' indicates anagramming the letters.
The final letter of 'moth' is 'h'.
'trapdoor' is an anagram of 'artropod'.
'h' placed within 'artropod' is 'ARTHROPOD'.
(Other definitions for arthropod that I've seen before include "Invertebrate" , "spider, for example" , "Such as a crustacean or spider" , "worker, perhaps" , "Creature such as insect or crustacean" .)