Large specimen unopened (7)
'large' is the definition.
(similar in meaning)
'specimen unopened' is the wordplay.
'specimen' becomes 'sample' (I've seen this before).
'unopened' means to remove the first letter (without opening letter).
'sample' with its initial letter taken away is 'AMPLE'.
(Other definitions for ample that I've seen before include "Large, capacious" , "Plentiful; capacious" , "Sealed glass container for dose of medicine" , "Fairly large" , "Large, accommodating" .)
'large specimen' is the definition.
'example' can be an answer for 'specimen' (I've seen this before). I am unsure of the 'large' bit.
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for example that I've seen before include "Specimen, illustration" , "warning" , "Something illustrating a general rule" , "Paradigm or model" , "Characteristic item" .)