Crossword Genius

Are out of a tin, but that’s the secret (6)

Ross

I believe the answer is:

arcane

Here is my best explanation:

'that's the secret' is the definition.
(thesaurus)

'are out of a tin' is the wordplay.
'out of' means one lot of letters goes inside another.
'a tin' becomes 'can' ('can' can be a synonym of 'tin').
'are' placed around 'can' is 'ARCANE'.

'but' acts as a link.

This clue was last seen in Evening Standard