Freed in error, Pierce is a spewer of venom (3-2-5)

I believe the answer is:

fer-de-lance

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'spewer of venom' is the definition.
The definition suggests a singular noun which matches the answer.

'freed in error pierce' is the wordplay.
'in error' indicates anagramming the letters.
'pierce' becomes 'lance' (lancing is a kind of piercing).
'freed' is an anagram of 'ferde'.
'ferde'+'lance'='FER-DE-LANCE'

'is a' is the link.

Can you help me to learn more?

(Another definition for fer-de-lance that I've seen is " Venomous American snake".)

I've seen this clue in The Guardian.

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