Unwelcome substance in canned beef? (5)
I believe the answer is:
toxin
'unwelcome substance' is the definition.
Although both the answer and definition are singular nouns, I can't understand how they can define each other.
'in canned beef?' is the wordplay.
'in' indicates putting letters inside.
'canned' becomes 'tin' (I can't justify this - if you can you should give a lot more credence to this answer).
'beef?' becomes 'ox'.
'tin' going around 'ox' is 'TOXIN'.
Can you help me to learn more?
(Other definitions for toxin that I've seen before include "Poison, venom" , "Form of poison" , "Poisonous substance" , "Natural poison" , "Poison of organic origin" .)