Pole and Eritrean held potential poisoner (8)
I believe the answer is:
oleander
'potential poisoner' is the definition.
Although both the answer and definition are singular nouns, I don't see how one could define the other.
'pole and eritrean held' is the wordplay.
'held' indicates a hidden word.
'OLEANDER' is hidden in the letters of 'pole and eritrean'.
Can you help me to learn more?
(Other definitions for oleander that I've seen before include "Flowering plant" , "Flowering shrub from olden era, oddly" , "'Adorn eel, badly, with this shrub (8)'" , "Mediterranean shrub" , "Red alone (anag.)" .)