Ambassador banned endless order for something poisonous (7)

I believe the answer is:

henbane

I'm a little stuck... Click here to teach me more about this clue!

'something poisonous' is the definition.
I can't judge whether this definition defines the answer.

'ambassador banned endless order' is the wordplay.
'ambassador' becomes 'HE' (His or Her Excellency).
'endless' means to remove the last letter.
'order' indicates an anagram.
'banned' with its last letter removed is 'banne'.
'banne' anagrammed gives 'nbane'.
'he'+'nbane'='HENBANE'

'for' is the link.

Can you help me to learn more?

(Other definitions for henbane that I've seen before include "poison" , "Poisonous plant" , "Poisoner" .)

I've seen this clue in The Daily Express.

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