Old fossil, one cast in 'Hackneyed' (9)

I believe the answer is:

trilobite

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'old fossil' is the definition.
'trilobite' can be an answer for 'fossil' (extinct creatures represented in the fossil record). I am not certain of the 'old' bit.

'one cast in hackneyed' is the wordplay.
'one' becomes 'i' (Roman numeral).
'cast' becomes 'lob'.
'in' is an insertion indicator.
'hackneyed' becomes 'trite' (synonyms).
'i'+'lob'='ilob'
'ilob' inserted inside 'trite' is 'TRILOBITE'.

Can you help me to learn more?

(Other definitions for trilobite that I've seen before include "Abundant fossil" , "find on Lyme Regis beach?" , "Fossil arthropod" , "Bitter oil (anag.)" , "one in rock" .)

I've seen this clue in The Guardian.

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