Rook into meat finds vein (6)
I believe the answer is:
streak
'vein' is the definition.
(I've seen this in another clue)
'rook into meat' is the wordplay.
I cannot quite understand how this works, but
'rook' could be 'r' (chess abbreviation) and 'r' is found in the answer.
'meat' could be 'steak' (steak is a kind of meat) and 'steak' is found within the remaining letters.
This accounts for all the letters.
This may be the basis of clue (or it may be nonsense).
'finds' is the link.
Can you help me to learn more?
(Other definitions for streak that I've seen before include "Long mark, run swiftly" , "One may be lucky" , "Run without clothes" , "Run naughtily naked" , "Stripe in the hair, say" .)